Many bird species express sexual dimorphism in body size, which is one of the most significant targets of natural and sexual selection, for it is tightly linked with fitness. During field studies in the breeding season of 2013 and 2014, we found significant differences in body morphometrics between sexes in a breeding population of Elliot's Laughingthrush Trochalopteron elliotii: males are larger than females in all body measurements. Positive assortative mating, based on culmen length, tarsus length and body mass, was found across breeding pairs. Male territory defence behaviour and assortative mating based on body size provide evidence that sexual selection may be responsible for sexual size dimorphism in this species.