With further decrease of the minimum features of interconnects, the Cu resistivity increases due to spatial confinement becomes an issue once again. However, compared with the superfilling ability, little attention has been paid to the resistivity increase originated from the additives of electroplating. In this work, the influence on the sheet resistance of Cu films electroplated with two levelers, 2-mercaptopyridine (2-MP) and Janus Green B (JGB), was studied in terms of impurity, morphology, grain size and crystalline structure. It was observed that the sheet resistance of the film deposited with 2-MP was higher than that with JGB both before and after self-annealing. During self-annealing, slight decrease of resistance was observed in the film deposited with 2-MP while great decrease occurred in the case of JGB. Although the type of impurity and texture of the two films were similar, differences were found in the morphology, grain size and amount of impurity (especially sulfur atoms). Therefore, the high resistance with 2-MP was attributed to the rough surface and fine grains in association with the plentiful sulfur atoms of 2-MP trapped in the Cu films.