In this paper, we investigate the asymmetric property of multiple-input multiple-output (MIMO) dual-hop amplify-and- forward (AF) relay networks. We consider the difference of the two hops in terms of both fading channels and scattering environment. In particular, we analyze the symbol error probability (SEP) of a MIMO orthogonal space-time block code (OSTBC) AF relay network in which the first and second hop undergo Rayleigh fading with a rich-scattering environment and Nakagami-m fading with a poor-scattering environment, respectively. Moreover, an asymptotic SEP expression yielding insights on the diversity gain is also obtained.