Background: Infertility is defined according to WHO is inability of couple to conceive during one year of marriage despite of not using contraception methods and regular sexual intercourse. Oligoasthenoteratozoospermia (OAT) syndrome refers to a condition of abnormally low sperm count, decrease motility and abnormal sperm morphology in the ejaculate. Objectives: To determine the seminal plasma Myeloperoxidase (MPO) level in OAT patients and normal controls and to correlate MPO level with semen parameters. Patients and Methods: This study was designed as a case control study. This study included 30 OAT patients, and 15 healthy individuals as a control group. MPO kit colorimetric method for in vitro was used to assess seminal level of MPO in OAT patients (45 informed consent). Results: There was a relation between MPO level and semen microscopic features like count, motility and morphology. Correlation of seminal MPO and semen parameters between two groups of smokers and varicocele. Correlation between seminal plasma MPO level and age. Relationship between smoking status and seminal plasma MPO among moderate and heavy smoking patients which was a statistically significance. Insignificant correlation between semen MPO level and degree of varicocele. Conclusions: The seminal plasma level of MPO was a significantly higher in patients with OAT. Relations between MPO and semen parameters could be considered as an essential biomarker for the inflammatory process in the body and active biomarker of oxidative stress status.