Abstract: To investigate the relationships between tilapia sizes and cold tolerance and select representative tilapia size for accurate evaluation of the cold tolerance, cold tolerance of tilapias with different sizes was investigated. In the condition of indoor artificial cooling, with 2益/d vertical cooling down to all the tilapias died, the lethal temperatures of 50%(LT50) of tilapias were determined by Logistic function. The results showed that, there was linear correlation between sizes and cold tolerance. We can choose tilapias with weight 8.7-12.0 g for the subsequent study.