The aim of this study is to investigate the effects of NO on sperm motility of ram. After incubation of normozoospermic samples for 160 min in the presence of L-arginine (NOS substrate), SNP (NO donor), L-NAME (non-selective nitric oxide inhibitor) and packed erythrocytes (NO scavenger), sperm motility assessed in four grades (A, B, C, D). In this study, L-arginine and SNP non-significantly increased progressive motility at low concentration and significantly decreased progressive motility at high concentration. L-NAME and packed erythrocytes dose-dependently decreased progressive sperm motility. It is concluded that sperm motility of ram physiologically depend on nitric oxide action although excess generation of nitric oxide by sperm or exogenous NO could not increase sperm motility and it seems that excess NO provides toxic condition to decrease sperm motility.