The algorithm for Detection of number of transmitting antennas plays an important role in design of intelligent receiver for interception of MIMO communications systems, because foremost it is necessary to know the number of transmitters. Since MDL is a standard solution for this problem, its performance analysis an important task. Previous works provide analysis in which the eigenvalues of covariance matrix of received signal are assumed to be known. Thus the impact of channel impairments on these eigenvalues and consequently the MDL performance is not studied. In this paper, the eigenvalues of covariance matrix of received signal are assumed to be unknown and the error probability of MDL is given based on the spatially correlated MIMO channel model using an estimation of channel eigenvalues. The accuracy of derived equations is evaluated using several simulations which show that the proposed analysis provides an acceptable prediction of MDL performance in different conditions.