We study the performance of space-time block coding in terms of different transmission matrices over Nakagami-m fading channels in multiple-input multipleoutput (MIMO) environments. A closed-form expression for the exact symbol error rate (SER) of orthogonal space-time block coding (OSTBC) over independent identically distributed Nakagami-m fading channels can be derived by means of the equivalent single-input single-output (SISO) model. The exact SERs of OSTBC with M-PSK and MQAM modulations are expressed in terms of the moment generating function (MGF) of instantaneous SNR as well as the higher transcendental functions. In this paper, we provide performance evaluation results of several codes of OSTBC with the closed-form expressions; also, Monte Carlo simulation results are given, which demonstrate the accuracy of closed-form solutions. In addition, some new observations on the performance results of different code matrices are made.