Fifth International Symposium on Signal Processing and its Applications,\ ISSPA'99, Brisbane, Australia, 22-25 August, 1999 Organized by the Signal Processing Research Center, QUT, Brisbane, Australia The blind separation of non stationary signals by only using the second order statistics. Ali MANSOUR BMC Research Center (RIKEN), 2271-130, Anagahora, Shimoshidami, Moriyama-ku, Nagoya 463 (JAPAN) Abstract "For the last 10 years, source separation has raised an increasing interest, partly because it has been discovered that space-time approaches will play an essential role in future radio communications" Lathauwer and Comon in {lathauwer-editsp-99}. In the case of instantaneous mixture (memoryless mixture or channel), many algorithms are proposed to solve the blind separation problem. In general case (where no special assumption is assumed), the high order statistics (i.e fourth order) are used in {lacoume-ica-99}. By adding special assumptions, algorithms and criteria can be simplified in {jutten-intsymp-95}. In this paper, we discuss and shortly present how the separation of non stationary signal can be done using only second order statistic. Keywords: Decorrelation, Second order Statistics, Whiteness, Blind separation of sources, natural gradient, Kullback-Leibler divergence.