Abstract: A composite population is a breed made up of two or more component breeds and designed to benefit from hybrid vigor without crossing with other breeds, and is thus regarded as an alternative method for heterosis utilization. The breeding effects depend on retained heterosis in livestock composites. This paper reviews prediction methods of retained heterosis, relative production efficiency and production performance, and evaluation methods of breeding effects of com-posite populations. A composite population contains all three types of heterosis. If inbreeding can be avoided, it can retain heterosis to a certain extent. The retained heterosis depends on the number of contributing breeds and their proportions in the composite. The production performance rests both on average breeding values of contributing breeds and on retained heterosis of the composite itself. Breeding effects of composite population can be evaluated by theoretical prediction, actual estimation of retained heterosis, examination of genetic variation and/or comparison with other relevant breeds.