Abstract: To study the effect of cold stress on biochemical parameters and ammonia nitrogen excretion of GIFT strain of Nile tilapia (Oreochromis niloticus), GIFT strain of Nile tilapia with an average weight of (232±10) g were cultured in water with temperature decrease speed of 1.0℃/h. The fish were randomly divided into two groups: a control group reared at water temperature of (24.5±0.2)℃ and a treatment group reared at water temperature of (14.3±0.8)℃. The experiments were repeated three times. Biochemical parameters and survival rate of the fish and pH , concentration of ammonia nitrogen in water were tested at 0, 4.5 and 24 h. The results showed that the concentration of blood glucose, muscle glycogen and lactic acid increased in the treatment group, compared with those in the control group at 0 h. Concentration of ammonia nitrogen in water also increased. However, the effect of cold stress on the fish decreased after 24 h. The results indicated that it might be safe to temporarily culture tilapia weighted around 200 g at the above temperature and temperature decrease speed.