The gonadal differentiation in fishes is affected by many environmental factors, among which temperature is one of the most important factors. In this paper, migration of primordial germ cells (PGCs), formation of genital ridge and gonadal differentiation were investigated using histological methods in Carassius auratus. Effects of different culturing water temperatures on the gonadal differentiation were also studied. Day 12 to day 40 was a sensitive period for the gonadal differentiation. From day 12 on, larvae were divided into 7 groups. Every group was cultured under one of seven temperatures for 28 days: 16±1℃, 20±1℃, 23-25℃, 27±1℃, 30±1℃, 32±1℃ and 34±1℃. The control group was cultured at 23-25℃. The results showed that larval sex ratio in the control group was approximately 1∶1 (female to male was 1∶1.07). In the 20±1℃ group, the larval sex ratio was also close to 1∶1 (1.09∶1). In the 27±1℃ group, female ratio increased and the female ratio could be as high as 55.3%(P<0.05). In lower temperature group 16±1℃, female to male was 1∶1.45, and the female ratio reached 40.8%. However, in the higher temperature groups, the female to male ratios were 6.14∶1, 2.51∶1 and 2.14∶1 when temperature was increased to 30±1℃, 32±1℃ and 34±1℃, respectively. The female ratio in 30±1℃ group was the highest, reaching as high as 86.0%. The temperature of 30±1℃ obviously induced feminization. These results suggest that sex determination in C.auratus is temperature-dependent sex determination (TSD). Nowadays, the global temperature become warmer, and the changing environmental factors lead to greenhouse effect, which might skew the sex ratio of C. auratus.