In this research, the influence of the drilling process parameters; three cutters (end mill) of different diameters, three of cutting speeds and five of feed rates on the process responses, i.e. the surface roughness ( ) and the delamination factor ( ) of the drilled hole are studied.  The two types of the used composites are GFRP and AL/SiCp. From the analysis of the results, the feed rate and the cutter diameter are had a large effect on surface roughness and delamination factor, while both of them are increased with the increase of cutter diameter and the used feed rates. The results of  surface roughness and the delamination factor when drilling GFRP composite are bigger than that values of AL/SiCp  composite  at all used cutters, cutting speeds and all used feed rates. Also, from the results, using of cutting speed (2500 rpm), end mill of the small diameter ϕ 8mm and low feed rate (10mm/min) are suitable for drilling GFRP and AL/SiCp to get a better surface roughness of the resulted.