We studied the diet of the Annulated Sea Snake (Hydrophis cyanocinctus) in the mangrove habitat of the Iranian Hara Protected Area. Prey items consumed by 34 individual snakes included four species of gobiid fish. Mudskippers (Periophthalmus waltoni, Boleophthalmus dussumieri, and Scartelaos tenuis) comprised the vast majority of the diet. All prey items were ingested head first. There was a positive correlation between snake SVL and total length of prey, but large snakes also ate small prey. Snake neck diameter was correlated positively with maximum prey diameter, and snakes did not consume prey items with a maximum diameter more than 1.2 times their neck diameter, a characteristic that may indicate gape limitation.