Abstract: In order to study the impact of oil spills on the Ulva Pertusa, one of the major macroalage in the intertidal zone of the coast, this study measured the growth rates, chlorophyll a as well as the carbon and nitrogen stable isotope of U.Pertusa under the stress of the water accommodated fraction (WAF) of 180# fuel oil.At the low WAF concentrations (1.43 mg/L, 2.87 mg/L and 4.30 mg/L), the growth rates of U.Pertusa were higher than the control group, indicating that the growth was promoted.Meanwhile, the contents of chlorophyll a increased, and carbon and nitrogen stable isotopes were enriched.However, at the high WAF concentrations (5.72 mg/L and 7.17 mg/L), the algal growth was inhibited, with the lower growth rates but higher concentrations of chlorophyll a than those in control group.In addition, compared to the control group, U.Pertusa showed the depletion in δ¹⁵N and δ¹³C at the high WAF concentrations.Overall, the carbon and nitrogen stable isotopes were more sensitive to the WAF stress than chlorophyll a for U.Pertusa.The present study indicated that δ¹⁵N and δ¹³C of U.Pertusa were the promising proxies to evaluate the toxicity of oil spill in marine environment.