|Location||Mullaitivu District, Sri Lanka
Trincomalee District, Sri Lanka
|Primary inflows||Churiyan Aru|
|Primary outflows||Indian Ocean|
|Surface area||29.95 square kilometres (11.56 sq mi)|
|Max. depth||4 metres (13 ft)|
|Surface elevation||Sea level|
Kokkilai lagoon (Tamil: கொக்குளாய்; Sinhalese: කෝකිලායි) is an estuarine lagoon in Mullaitivu District and Trincomalee District, north-east Sri Lanka. The town of Kokkilai is located on a sand bar between the lagoon and the Indian Ocean.
The lagoon has extensive sea grass beds and small areas of mangrove swamp and mudflats. The shallow waters of the lagoon attracts a wide variety of water birds including pelican, cormorant, herons, egrets, wild duck, stork, waders and pink flamingoes.
The lagoon was designated a wildlife sanctuary in 1951.