Five isonitrogenous and isolipidic fattening diets were formulated by blending vegetable oils (soybean oil: rapeseed oil = 1︰1) to replace fish oil at level of 0, 25%, 50%, 75% and 100% (named as diet F1, F2, F3, F4 and F5, Table 1) to feed 5 treatments of adult male Chinese Mitten Crab (Eriocheir sinensis) for 60 days. Then, we assayed the proximate composition and fatty acid composition of the hepatopancreas, muscle and testis of each crab in the five treatments and analyzed these data by variance analysis method. We got the following results: (1) The gonads of crabs fed F1 diet had the significantly higher ash content than those fed by diet F4 and F5 (P < 0.05), but no significant difference with crabs fed diet F2 and F3; no significant differences in the contents of moisture, crude protein and crude lipid among five diet treatments (P > 0.05). The contents of moisture and ash in the hepatopancreas of crabs fed diet F1 were highest among the five treatment group, but the crude lipid was lower than other four treatments; however, no significant difference was found in the crude protein content between individuals in the five treatments (P > 0.05). Except for the crabs treated by diet F1, the crude lipid and ash contents in the muscle increased with increasing replacement level; while no significant differences were found for the rest contents in the muscle among crabs treated by five diet (P > 0.05) (Table 3). (2) The total n-6 polyunsaturated fatty acid (∑ n-6PUFA) contents in gonads of crabs increased with the increasing replacement level, while the content of total n-3 polyunsaturated fatty acid (∑ n-3PUFA) had opposite changing tendency. No significant difference was found in the total saturated fatty acid (∑ SFA), total polyunsaturated fatty acid (∑ PUFA) and total highly unsaturated fatty acid (∑ HUFA) contents in the crab gonads between all the five treatments (P > 0.05) (Table 4). (3) The highest content of ∑ n-3PUFA and ∑ HUFA was detected in the hepatopancreas of crabs treated by diet F3 although there was a significant difference between each treatment. While no significant differences were found for the ∑ PUFA and ∑ n-6PUFA contents among five treatments (P > 0.05) (Table 5). (4) There was no significant difference among the fatty acids contents in muscle except for the content of ∑ n-6PUFA which increased with elevating replacement levels (Table 6). In conclusion, except for moisture and crude protein contents, fish oil replacement by blending vegetable oils in fattening diets have significant influence on fatty acid composition in the edible tissues of adult male E. sinensis. These results suggested that the replacement level of 50% is good for the fat accumulation in the hepatopancreas and muscle of this crab.