Abstract: The present experiment was designed to investigate the protein requirement of mandarin fish (Siniperca chuatsi). Six isoenergetic (the gross energy was about 20MJ/kg) diets contained different protein level (32.61%、38.10%、43.55%、 48.95%、 53.64%、56.30% ) were formulated. The experiment was conducted in the net enclosure of cement pool and lasted 41 days. The mean initial weight of mandarin fish was 65.00±2.25. The mean temperature of water was 22.5℃ during the experiment. The result of the experiment showed that the SGR(specific growth rate) of mandarin fish increased with the increasing of protein content in the diets. But when the protein content in diet reached 48.95%,the SGR of mandarin fish decreased slowly. The SGR of group 32.61% and group 38.1% were significant lower than the other four groups(P0.05). And the SGR of group had no significant difference(P0.05). The change of the PER (protein efficiency ratio) of mandarin fish showed the parabola shape,the regression function of PER(Y) and protein content(X) was Y=-0.148X 2+13.104X-176.120 (R= 0.9602 P0.01 ) . When the PER reached max,the corresponding protein content of diet was 44.27%. So,in broken-line module,the most proper protein contenl of mandarin fish formulated diet was 44.27%-48.41%.