Aluminum has been increasingly used in automotive and aerospace applications due to its beneficial specific strength and chemical properties. Due to its extensive use, machining of aluminum parts has become specifically significant in recent years. One important aspect of machining is the surface quality represented by the surface roughness values. In this article, the effect of equal-channel angular pressing on the surface roughness (R_a, R_q, R_t and R_z) of commercial purity aluminum machined by turning was studied. Five starting material conditions, defined as the annealed and equal-channel angular pressing processed up to four passes, were investigated. The independent variables were the cutting speed, depth of cut and feed rate. The fourth parameter (number of equal-channel angular pressing passes) was considered as categorical factor and, hence, was not included in the mathematical model. A full central composite circumscribed design matrix was built to allow the optimization of surface roughness using response surface methodology. The significance of process parameters and their interactions in estimating surface roughness was investigated using analysis of variance. The two parameters, with significant effect on surface roughness, were found to be the feed rate and number of equal-channel angular pressing passes. Minimum depth of cut (0.15 mm) and minimum feed rate (0.05 mm/rev) are needed to achieve minimum surface roughness parameters: R_a (0.06 µm), R_q (0.057 µm) and R_z (0.71 µm) and R_t (1.2 µm). The cutting speed, for these optimum roughness values, ranged from 207.5 m/min for R_a to 193 m/min for R_z. The optimum roughness values were generally achieved with the higher strength materials. Optimum values for R_a, R_q and R_z happened at the four equal-channel angular pressing passes–processed material, while the optimum value of R_t happened at the three equal-channel angular pressing passes–processed material.