This paper shows an optimization study on optimum determination of the cutting parameters and cutter helix angle when end milling of Al6061. In this study, the effects of the milling process parameters and tool geometry, including the cutting velocity, feed rate, radial depth of cut, and cutter helix angle. Moreover, in order to estimate the influences of these factors on the optimum cutting parameters and helix angle, a simulation experiment was designed and conducted by a computer program. A regression equation was proposed to calculate the optimum cutting speed, feed rate, radial depth of cut, and cutter helix angle.The Particle swarm optimization algorithm (PSO) was proposed to obtain the optimal parameters in consideration of the boundary conditions, which are determined from the empirical relationship of factors affecting the machining process