The aim of this study was to determine the level of malondialdehyde in seminal plasma of fertile and infertile men and investigate its relationship with sperm quality. Results showed that the mean of ± S.D. MDA concentration in seminal plasma of infertile men (0.94 ± 0.28 nmol/ml) was significantly higher than fertile men (0.65 ± 0.17 nmol/ml) (p value< 0.001), and had negative relationship with sperm count, motility and morphology. Therefore it could be concluded that increase in lipid peroxidation was associated with sperm membrane destructed and high level of MDA.