Trincomalee Bay, also known as Koddiyar Bay, is a bay in the Eastern Province, Sri Lanka. The bay is located by Trincomalee town on the north-east coast of the island.

Trincomalee Bay is open towards the northeast and has three differentiated parts. The main bay, also known as Koddiyar Bay, is located in the south and southeastern side and fairly regularly shaped, as well as enclosed and deep, forming a large natural harbour in the shores of the Indian Ocean. The commercial harbour is located in the 5 km (3 mi) long and 4 km (2 mi) wide northern indentation, also known as China Bay, on whose western side lies China Bay Airport. Tambalagam Bay is a mostly shallow western indentation of the main bay stretching westwards for 8 km (5 mi).

The bay is overlooked by terraced hills in the northwest and its entrance is guarded by two headlands. Trincomalee Bay has a length of 13 km (8 mi) and a width of 10 km (6 mi), while the mouth of the bay is 5 km (3 mi) wide.

The bay includes a few islands: Round Island, Elephant Island and Clappenburg Island in the main bay, and Great Sober Island and Little Sober Island in China Bay. The latter two are wildlife sanctuaries

Trincomalee Harbour, formerly a naval base of the Royal Navy, was taken over by the Sri Lankan Government in 1956 to be developed as a commercial port. The base in Trincomalee was fitted out to perform slipway repairs for the Sri Lanka Navy.

• Kinniya Bridge
• List of islands of Sri Lanka
• Round Island Light, Sri Lanka

• Media related to Trincomalee Bay at Wikimedia Commons