Space-time coding has been well documented as an attractive means to achieve high data rate transmissions. The paper investigates space-time block coded (STBC) OFDM systems in unknown multipath fading channels using a pilot embedded (PE) technique. The PE technique superimposes periodic training-sequences on information-bearing signals at a low power. There is no loss in information rate. Employing first-order statistics, it enables a closed-form channel estimation algorithm to track slowly time-varying channels. A mean-square-error (MSE) bound is derived to evaluate the proposed channel estimator. Computer simulation examples are presented to demonstrate MSE and overall system performances in the presence of unknown multipath fading channels.