One of the designers concerns is structural failure as a result of stress concentration in the geometrical discontinuities. Stress concentration factor in the presence of cutout, is a key parameter in reducing the structural load-bearing capacity. In the analysis of perforated isotropic plates, the effective parameters on stress distribution around cutouts are the cutout geometry, curvature radius of cutout corner, rotation angle of cutout and load angle. In this study, using PSO method it has been tried to introduce the optimum parameters to achieve the minimum amount of stress around the n-sided cutouts in isotropic plates under uniaxial tension. In this paper, an analytical method has been used to calculate the stress around cutouts with different shapes. According to this method, by using the conformal mapping, Muskhelishvili’s complex variable method which is only for circular and elliptical cutouts, has been developed for the other cutouts. The results presented in this case shows that by choosing the appropriate shape of cutout and the optimal effective parameters, stress concentration factor can be significantly reduced and lowest stress concentration factor rather than amount of stress concentration corresponding to circular hole can be achieved.