Peracetic acid may become one of alternative non-chlorine bleaching chemicals in the production of fully bleached chemical pulps. In this paper, the stability of peracetic acid was studied in an aqueous solution under conditions most likely encountered in the industrial processes. It was found that three potential reactions, namely i) the spontaneous decomposition,) the hydrolysis and iii) the transition metal catalyzed decomposition, are responsible for the consumption of peracetic acid. Furthermore, the kinetics of the spontaneous decomposition was developed. It was found that the reaction follows a second-order kinetics with the maximum rate at pH 8.2, which is the pK(a) of peracetic acid. Finally, the developed kinetic equation can describe very well the experimental results obtained in this study as well as the earlier data from Koubek (1964).