Heat transfer characteristics of an anodized two-phase closed thermosyphon (TPCT) with refrigerant as the working fluid is studied and compared with that of a non-anodized one. A simple anodization is performed to make a porous structure on the inner wall of TPCT. The anodized and non-anodized TPCTs charged with a blend of R600a and R290 are tested for the heat input range of 50-200W. The effects of filling ratio, inclination angle, heat input and anodized surface on the performance of the TPCTs are investigated. Due to the anodization, the evaporator heat transfer coefficient enhances up to 33% at the inclination angle of 450 for the heat input of 200 W. Also, total thermal resistance of the anodized TPCT is reduced by 17%, 20% and 23% respectively for horizontal, inclined and vertical positions when compared to the non-anodized TPCT. Enhancements in the surface area, number of nucleation sites, increased bubble frequency, intensified bubble interaction and thin film evaporation are major factors for the performance enhancement in the anodized TPCT. Also it is found that the filling ratio, inclination angle and heat input have a significant role on the performance of the TPCT. (C) 2014 Elsevier Ltd. All rights reserved.