The relationship between semen hyper viscosity and oxidative stress in infertile male by measuring Malondialgehyde (MDA) as a biomarker of oxidative stress and paraoxonase-1 (PON-1) as an antioxidant agent in hyper viscid semen. Hyper viscid Samples was collected from 60 infertile patients who attended the outpatient clinic of andrology department in Kasr AL-Ainy hospitals; divided into three main groups age matched , each 20 cases as Azoospermic, Oligo and/or Asthenozoospermic and Normozoospermic patients. The samples were subjected to semen fluid analysis according to WHO criteria of 2010 to determine the viscosity and other parameters of semen.Then the samples were centrifuged and seminal plasma was separated and freezed in a temperature -70C without preservative for one or two months and then measure the level of oxidative stress in form of malondialdehyde (MDA) and anti-oxidant capacity in form of paraxonase-1 (PON-1). The patients were selected after exclusion criteria such as lukocytospermia, smoking, alcohol intake, chronic diseases and anti-oxidant therapy. The level of MDA showed a highly significant increase in the Azoospermic as compared to Normozoospermic groups (p = 0.006), and again it is highly significant increase in Oligo and/or Asthenozoospermic when compared to Normozoospermic cases (p <0.001). Similarly, the level of PON-1 showed a highly significant decrease in Azoospermic as compared to Normozoospermic groups (p = 0.001) . PON-1 also high significantly decrease in Oligo and/or Asthenozoospermic as compared to Normozoospermic cases. A significant difference between the three study groups regarding the grade of viscosity was found. A significant negative correlation between MDA and PON-1 in the three study groups was found. A significant inverse relationship was elicited between the levels of PON-1and the percentage of abnormal forms of sperm among Oligo and/or Asthenozoospermic cases. Among patients with grade (2) hyper viscosity a highly significant difference was elicited between Normozoospermic and Oligo and/or Asthenozoospermic groups regarding both MDA (p =0.005) and PON-1 (p =0.002) as showed in table (6). MDA level shows a highly significant increase in Azoospermic as compared to Normozoospermic groups as well as in Oligo and/or Asthenozoospermic as compared to Normozoospermic cases. There is no significant correlation between MDA level and semen parameters in form of count, motility and morphology whether in Normozoospermic or Oligo and/or Asthenozoospermic cases.PON-1 also there is a highly significant decreasing in Azoospermic as compared to Normozoospermic groupsin one hand and in Oligoand/or Asthenozoospermic as compared to Normozoospermic groups in another hand. An inverse relationship between MDA as a biomarker of OS and PON-1 as an indicator of TAC in the three study groups was noted. Also there is a significant negative correlation between PON-1 and abnormal forms percent within Oligo and/or Asthenozoospermic cases. For semenhyper viscosity we demonsted a significant difference between the three study groups regarding the grade of viscosity. A highly significant difference was elicited between Normozoospermic and Oligo and/or Asthenozoospermic groups regarding both MDA and PON-1 among grade (2) hyper viscosity; this may indicate that OS may be a precipitating or a causative factor which may play a role in semen hyper viscosity.