An on line blind source separation (BSS) algorithm is presented in this paper under the assumption that sources are temporarily correlated signals. By using only some of the observed samples in a recursive calculation, the whitening matrix and the rotation matrix could be approximately obtained through the measurement of only one cost function. Simulations show good performance of the algorithm. An on line blind source separation (BSS) algorithm is presented in this paper under the assumption that sources are temporarily correlated signals. By using only some of the observed samples in a recursive calculation, the whitening matrix and the rotation matrix could be substantially-obtained through the measurement of only one cost function. Simulations show good performance of the algorithm.