The objective of this paper is to generate a mathematical model in order to minimize the value of surface roughness (Ra) through EDM by constructing an objective function consisting of combination of process parameters. Taguchi orthogonal design method of experiments with three process parameters viz., current, pulse-on-rate, pulse-off-rate were used to generate 25 numbers of experiments L25 at five levels. Experiments were carried out in Electronica S50 (CNC) EDM. Data obtained for performance measurement was subjected regression analysis using ANOVA. Equation was obtained for the surface roughness as a function of current, pulse-on rate, pulse-off-rate.It is found that discharge current, pulse-on-rate, and pulse-off-rate have significant effect on the Ra. Higher values of current and pulse-on-rate increased surface roughness. Lower current, lower pulse-on-rate and relatively higher pulse-off-rate produced a better surface finish.