The petroleum hydrocarbon concentrations in seawater were 0.05 mg/L, 0.30 mg/L, 0.50 mg/L, and 1.00 mg/Lseparately. Three replicates were designed for each treatment. The experimental period for the scallop, Chlamys farreri,was 30 days. Sampling occurred at hours 0 and 12 and days 1, 3, 6, 10, 15, 21, and 30. The gills, digestive gland, andhemocytes were stored at −80℃ and were evaluated within 24 h. The results showed that none of the biomarkerschanged significantly in the 0.05 mg/L group. Alkaline phosphatase (ALP), superoxide dismutase, and glutathione peroxidaseactivities increased significantly in the gills and digestive glands of the 0.30 mg/L and 0.50 mg/L groups(P<0.05), whereas these activities were similar to or lower than control levels in the 1.00 mg/L group. Biomarkers in thegills changed more significantly than those of the digestive gland. Hemocyte membrane stability did not change significantlyin the 0.05 mg/L group but was lower than that in the controls and other groups later in the experiment(P<0.05). Hemocyte stability was lower in the groups exposed to higher petroleum hydrocarbon concentrations.Theseresults suggest that C. farreri can detoxify low concentrations of petroleum hydrocarbon, such as 0.05 mg/L. No effecton hemocyte stability was observed over the short term in the 0.30 mg/L and 0.50 mg/L groups, but oxidative damageoccurred later in the experiment, which decreased membrane stability. The C. farreri biomarkers changed significantlyin the 1.00 mg/L petroleum hydrocarbon concentration group and oxidative damage to the gills increased and hemocytemembrane stability decreased substantially after 3 d. Antioxidant and ALP activities changed significantly in the gillscompared to those in the digestive gland at the same petroleum hydrocarbon concentration, so the gills were more sensitiveto petroleum hydrocarbon than the digestive gland. The changes in the biomarkers showed dose- and time-effectcharacteristics; thus, these biomarkers may be useful to evaluate oceanic oil pollution.