The current study aims to investigate the relationship between lipid peroxidation, represented by seminal malondialdehyde (MDA) level, and integrity of sperm plasma membrane, represented by the hypo-osmotic swelling (HOS) test score, in infertile men. One hundred and twenty Iraqi men (20 fertile and 100 infertile) shared in this study during their attendance to the High Institute for Infertility Diagnosis and Assisted Reproductive Technologies/Al- Nahrain University. The mean age of the fertile men was (30.46±0.78) years while the mean age of infertile men was (32.58±0.64) years with the duration of infertility (5.36±0.33) years. Semen samples were collected and the parameters of seminal fluid analysis were assessed; also, the HOS test score and seminal MDA level were determined. The results showed a significant (P<0.05) decrease in sperm concentration, sperm motility, sperm grade activity (progressive sperm motility and non-progressive sperm motility), total progressive sperm and normal sperm morphology with a significant (P<0.05) increase in sperm agglutination and round cells count in the infertile group compared with the fertile group. The percentage of sperm HOS test score in the infertile men was significantly (P<0.05) lower than that in the fertile men while seminal MDA level in the infertile men was significantly (P<0.05) higher than in the fertile men. Also, the results revealed a significant negative correlation (r = -0.48, P<0.05) between HOS test score and seminal MDA level in the infertile men. In conclusion, increased seminal MDA levels together with poor response of spermatozoa to hypo-osmotic stress in infertile men could represent the pathological impact of lipid peroxidation on the spermatozoa membrane and consequently on sperm function and quality. Lipid peroxidation may alter sperm membrane functional intergrity adversely and contribute to abnormal sperm function.