Abstract: Stable isotope analysis has been considered to be a powerful tool to investigate the food web structure of marine ecosystems and to quantify the trophic position of marine organisms.In this study, the stable carbon and nitrogen isotope values of organisms in the Haizhou bay were measured and their trophic levels were estimated.Results showed that the range of fish stable carbon and nitrogen isotope values were-16.2 ‰~-23.3‰ and 9.6‰~13.9‰, respectively.The trophic levels of fish species ranged from 1.9 to 3.9, with top predators Lateolabrax maculatus and Trypauchen vagina occupied the highest trophic level and the primary consumers Sinonovacula constricta and Acetes chinensis having the lowest ones.There was a significant positive relationship between body size and stable nitrogen isotope values for Oratosquilla oratoria exist, indicating an ontogenetic trophic shift during growth(R²=0.90, P < 0.01).The carbon isotope values of organisms in Haizhou Bay suggested a large overlap in trophic niche among species.