diff --git a/azalea-client/src/client.rs b/azalea-client/src/client.rs
index 364abef6..dfefe4ad 100644
--- a/azalea-client/src/client.rs
+++ b/azalea-client/src/client.rs
@@ -600,6 +600,9 @@ impl Client {
             GamePacket::ClientboundSetEquipmentPacket(p) => {
                 println!("Got set equipment packet {:?}", p);
             }
+            GamePacket::ClientboundUpdateMobEffectPacket(p) => {
+                println!("Got update mob effect packet {:?}", p);
+            }
             _ => panic!("Unexpected packet {:?}", packet),
         }
 
diff --git a/azalea-protocol/src/packets/game/clientbound_update_mob_effect_packet.rs b/azalea-protocol/src/packets/game/clientbound_update_mob_effect_packet.rs
new file mode 100644
index 00000000..5a446c2f
--- /dev/null
+++ b/azalea-protocol/src/packets/game/clientbound_update_mob_effect_packet.rs
@@ -0,0 +1,16 @@
+use azalea_buf::McBuf;
+use packet_macros::GamePacket;
+
+#[derive(Clone, Debug, McBuf, GamePacket)]
+pub struct ClientboundUpdateMobEffectPacket {
+    #[var]
+    pub entity_id: u32,
+    // TODO: have an enum for this
+    #[var]
+    pub effect: u32,
+    pub effect_amplifier: u8,
+    #[var]
+    pub effect_duration_ticks: u32,
+    pub flags: u8,
+    pub factor_data: Option<azalea_nbt::Tag>,
+}
diff --git a/azalea-protocol/src/packets/game/mod.rs b/azalea-protocol/src/packets/game/mod.rs
index 3e492dec..f407a697 100755
--- a/azalea-protocol/src/packets/game/mod.rs
+++ b/azalea-protocol/src/packets/game/mod.rs
@@ -46,6 +46,7 @@ pub mod clientbound_system_chat_packet;
 pub mod clientbound_teleport_entity_packet;
 pub mod clientbound_update_advancements_packet;
 pub mod clientbound_update_attributes_packet;
+pub mod clientbound_update_mob_effect_packet;
 pub mod clientbound_update_recipes_packet;
 pub mod clientbound_update_tags_packet;
 pub mod clientbound_update_view_distance_packet;
@@ -124,6 +125,7 @@ declare_state_packets!(
         0x63: clientbound_teleport_entity_packet::ClientboundTeleportEntityPacket,
         0x64: clientbound_update_advancements_packet::ClientboundUpdateAdvancementsPacket,
         0x65: clientbound_update_attributes_packet::ClientboundUpdateAttributesPacket,
+        0x66: clientbound_update_mob_effect_packet::ClientboundUpdateMobEffectPacket,
         0x67: clientbound_update_recipes_packet::ClientboundUpdateRecipesPacket,
         0x68: clientbound_update_tags_packet::ClientboundUpdateTagsPacket,
     }