diff --git a/src/function/as_geojson.rs b/src/function/as_geojson.rs
new file mode 100644
index 0000000..80c1605
--- /dev/null
+++ b/src/function/as_geojson.rs
@@ -0,0 +1,145 @@
+use crate::geo::GeometryArray;
+use crate::DFResult;
+use arrow_array::cast::AsArray;
+use arrow_array::{GenericBinaryArray, LargeStringArray, OffsetSizeTrait, StringArray};
+use arrow_schema::DataType;
+use datafusion_common::{internal_datafusion_err, DataFusionError};
+use datafusion_expr::{ColumnarValue, ScalarUDFImpl, Signature, TypeSignature, Volatility};
+use geozero::ToJson;
+use std::any::Any;
+use std::sync::Arc;
+
+#[derive(Debug)]
+pub struct AsGeoJsonUdf {
+    signature: Signature,
+    aliases: Vec<String>,
+}
+
+impl AsGeoJsonUdf {
+    pub fn new() -> Self {
+        Self {
+            signature: Signature::one_of(
+                vec![
+                    TypeSignature::Exact(vec![DataType::Binary]),
+                    TypeSignature::Exact(vec![DataType::LargeBinary]),
+                ],
+                Volatility::Immutable,
+            ),
+            aliases: vec!["st_asgeojson".to_string()],
+        }
+    }
+}
+
+impl ScalarUDFImpl for AsGeoJsonUdf {
+    fn as_any(&self) -> &dyn Any {
+        self
+    }
+
+    fn name(&self) -> &str {
+        "ST_AsGeoJSON"
+    }
+
+    fn signature(&self) -> &Signature {
+        &self.signature
+    }
+
+    fn return_type(&self, arg_types: &[DataType]) -> datafusion_common::Result<DataType> {
+        match arg_types[0] {
+            DataType::Binary => Ok(DataType::Utf8),
+            DataType::LargeBinary => Ok(DataType::LargeUtf8),
+            _ => unreachable!(),
+        }
+    }
+
+    fn invoke(&self, args: &[ColumnarValue]) -> datafusion_common::Result<ColumnarValue> {
+        let arr = args[0].clone().into_array(1)?;
+        match args[0].data_type() {
+            DataType::Binary => {
+                let wkb_arr = arr.as_binary::<i32>();
+
+                let mut json_vec = vec![];
+                for i in 0..wkb_arr.geom_len() {
+                    json_vec.push(to_geojson::<i32>(wkb_arr, i)?);
+                }
+
+                Ok(ColumnarValue::Array(Arc::new(StringArray::from(json_vec))))
+            }
+            DataType::LargeBinary => {
+                let wkb_arr = arr.as_binary::<i64>();
+
+                let mut json_vec = vec![];
+                for i in 0..wkb_arr.geom_len() {
+                    json_vec.push(to_geojson::<i64>(wkb_arr, i)?);
+                }
+
+                Ok(ColumnarValue::Array(Arc::new(LargeStringArray::from(
+                    json_vec,
+                ))))
+            }
+            _ => unreachable!(),
+        }
+    }
+
+    fn aliases(&self) -> &[String] {
+        &self.aliases
+    }
+}
+
+fn to_geojson<O: OffsetSizeTrait>(
+    wkb_arr: &GenericBinaryArray<O>,
+    geom_index: usize,
+) -> DFResult<Option<String>> {
+    let geom = {
+        #[cfg(feature = "geos")]
+        {
+            wkb_arr.geos_value(geom_index)?
+        }
+        #[cfg(not(feature = "geos"))]
+        {
+            wkb_arr.geo_value(geom_index)?
+        }
+    };
+    let json = match geom {
+        Some(geom) => Some(
+            geom.to_json()
+                .map_err(|_| internal_datafusion_err!("Failed to convert geometry to geo json"))?,
+        ),
+        None => None,
+    };
+    Ok(json)
+}
+
+impl Default for AsGeoJsonUdf {
+    fn default() -> Self {
+        Self::new()
+    }
+}
+
+#[cfg(test)]
+mod tests {
+    use crate::function::{AsGeoJsonUdf, GeomFromTextUdf};
+    use arrow::util::pretty::pretty_format_batches;
+    use datafusion::logical_expr::ScalarUDF;
+    use datafusion::prelude::SessionContext;
+
+    #[tokio::test]
+    async fn as_geojson() {
+        let ctx = SessionContext::new();
+        ctx.register_udf(ScalarUDF::from(GeomFromTextUdf::new()));
+        ctx.register_udf(ScalarUDF::from(AsGeoJsonUdf::new()));
+        let df = ctx
+            .sql("select ST_AsGeoJSON(ST_GeomFromText('POINT(-71.064544 42.28787)'))")
+            .await
+            .unwrap();
+        assert_eq!(
+            pretty_format_batches(&df.collect().await.unwrap())
+                .unwrap()
+                .to_string(),
+            "+-------------------------------------------------------------------+
+| ST_AsGeoJSON(ST_GeomFromText(Utf8(\"POINT(-71.064544 42.28787)\"))) |
++-------------------------------------------------------------------+
+| {\"type\": \"Point\", \"coordinates\": [-71.064544,42.28787]}           |
++-------------------------------------------------------------------+"
+        );
+    }
+}
diff --git a/src/function/mod.rs b/src/function/mod.rs
index 38c25be..622b0db 100644
--- a/src/function/mod.rs
+++ b/src/function/mod.rs
@@ -1,5 +1,6 @@
 #[cfg(feature = "geos")]
 mod as_ewkt;
+mod as_geojson;
 mod as_text;
 mod box2d;
 #[cfg(feature = "geos")]
@@ -23,6 +24,7 @@ mod translate;
 
 #[cfg(feature = "geos")]
 pub use as_ewkt::*;
+pub use as_geojson::*;
 pub use as_text::*;
 #[cfg(feature = "geos")]
 pub use covered_by::*;