Abstract: Swimming crab (Portunus trituberculatus) is an important mariculture crab, and the light color of the pond-reared crabs may be related to low level of dietary astaxanthin. This study was designed to investigate the effects of dietary astaxanthin on ovarian development, coloration, antioxidant capacity, immune performance and biochemical composition of female P. trituberculatus. Haematococcus pluvialis powder was used as natural astaxanthin source to formulate four experimental diets with different astaxanthin levels (0, 26.60, 41.62, and 81.37 mg/kg, defined as Diet 1#—4#). The four experimental diets were fed to female P. trituberculatus for 45 days during the ovarian development; therefore, there were four treatments in this study. The results showed as follows: (1) Dietary astaxanthin had no significant effects on gonadosomatic index (GSI) and hepatosomatic index (HSI). (2) Total carotenoids content, redness (a*) and yellowness (b*) values of hepatopancreas, ovaries and carapace increased significantly with increasing dietary astaxanthin, while the lightness (L*) values of these tissues showed a decreasing trend (P<0.05). (3) For antioxidant indices, the activities of super oxide dismutase (SOD) and peroxidase (POD) in treatments (Diet 2#—4#) with supplementation of astaxanthin were significantly lower than those in Diet 1# treatment without supplementation of astaxanthin. The activities of total antioxidant capacity (T-AOC) and glutathione peroxidase (GSH-Px) in hemolymph as well as the SOD, T-AOC in hepatopancreas increased significantly with elevated dietary astaxanthin, while a decreasing trend was found for the malondialdehyde (MDA) content in the hemolymph and hepatopancreas. (4) For the immune indices, Diet 4# treatment had the highest activity of acid phosphatase (ACP) in hemolymph and hepatopancreas, while Diet 1# treatment had the significantly higher hemolymph hemocyanin (Hc) content than other treatments (P<0.05). (5) As for the biochemical composition, the increasing trend was found on the contents of total lipids and total carbohydrate in the muscle and hepatopancreas as well as ovarian lipids with increasing dietary astaxanthin, while Diet 2# treatment had the highest total carbohydrate content in the ovaries among the four treatments (P<0.05). In conclusion, dietary supplementation of astaxanthin had no significant effect on ovarian development ofP. trituberculatus, but could improve the coloration, antioxidant capacity and the contents of total lipids and total carbohydrate in edible tissues. These results suggest the appropriate level of astaxanthin in fattening diet was approximately 50 mg/kg for adult female P. trituberculatus.