Abstract: The aim of this study was in vitro evaluation of antiseptic effect of different concentrations of Peroxy Acetic Acid (PAA) as percidine and percidine 513 on Microsporum gypseum, Candida albicans and Aspergillus niger. Standard strains (PTCC) were cultured on malt extract agar medium. Fungal suspensions were prepared containing 4x107 cfu mL-1 conidia and yeast cells. Afterward, they were treated with 1, 3, 5, 10 and 20% of percidine in 3, 5, 10, 20, 30 min and 0.2% of percidine 513 in 3, 5, 15, 30, 45, 60 min. Eventually, the number of conidia and yeast cells were counted. The numbers of colonies were also counted after culturing the treated suspensions on malt extract agar medium. On the basis of protocol 6986 of Institute of Standards and Industrial Research of IRAN (ISIR), a logarithmic reduction of 104 in vegetative conidia will reflects the effectiveness of the studied substrate. For C. albicans and M.gypseum, the satisfactory results were obtained by using 1 and 3% of percidine after 10 min. However, in case of percidine 5%, the aim was obtained after 3 min. On the other hands, in case of A. niger, acceptable results were obtained after 20 min for percidine 3%, 10 min for percidine 5 and 10% and finally 5 min for percidine 20%. According to ISIR, PAA can be considered as a reliable antiseptic for using in general application due to its high potency for reducing the intensity of microbial population specially the most important species of fungi.