Abstract: By lowering the water temperature progressively with an LKB thermostatic circulator, we studied comparatively the low temperature tolerance of mud carp (Cirrhina molitorella)and mixed sperm (from grass carp and mud carp or from grass carp silver carp, red common carp and mud carp) inseminated mud carp of the second successive generation. The mixed sperm inseminated mud carp of the successive generation were more tolerant of low temperature than mud carp both in terms of the enduring time at 7℃ and of the low temperature limits for shock and death. However, the improvement is rather limited. We proposed, therefore, the mixed sperm insemination method is unable to improve the mud carp's low temperature endurance below 6℃ and other breeding methods must be explored in order to improve the cold tolerance of this fish more effectively.