Objective:To evaluate the effect of thermal cycling on surface roughness of three different types of nickel titanium (NiTi) orthodontic wires. Materials and Methods: A total of 60 NiTi wire specimens were used in this study and equally divided into 3 groups according to type of wire; Group I: Supper elastic NiTi wire, Group II: Thermo-activated NiTi wire, and Group III: Copper NiTi super elastic at 27^oC wire (27^oC CuNiTi).  Each group was subdivided into 4 equal subgroups 1, 2, 3, and 4. In subgroup 1, specimens were not subjected to thermal cycles (control group). In subgroups 2, 3, and 4, specimens were subjected to 833, 1666, and 2500 thermal cycles respectively. Profilometer and atomic force microscope (AFM) were used to evaluate the surface roughness for all studied wires. The data were analyzed using analysis of variance (ANOVA test) and Post-hoc Tukey test. Results: There was a significant increase in surface roughness of super elastic NiTi wires after 2500 thermal cycles (p < 0.05). While surface roughness was in significant increased for either 27^oC CuNiTi or thermo-activated NiTi wires (p>0.05). The surface roughness of all tested NiTi wires showed obvious indentation and pitting on the surface of wire after thermal cycling. Conclusion: Thermal aging for three months (2500 thermal cycles) significantly increased the surface roughness of super elastic NiTi wire. On the other hand, thermal aging for three months had no pronounce effect for either 27^oC CuNiTi or thermo-activated NiTi wires. KEY WORDS: Thermal cycling, NiTi wires, Surface roughness.