Background: Oxidative stress is the result of an imbalance between the production and scavenging of reactive oxygen species (ROS). Recently, oxidative stress has been introduced as a major cause of male infertility. Objectives: The aim of the present study was to determine the correlation between total antioxidant capacity (TAC) and malondialdehyde (MDA) as markers of oxidative stress in relation to idiopathic male infertility and sperm parameters. Patients and Methods: This case control study was conducted using 35 men with idiopathic infertility and 34 men with proven fertility. Seminal plasma TAC and MDA were measured by ferric reducing ability of plasma (FRAP) and thiobarbituric acid (TBA) reaction methods, respectively. Results: Seminal TAC levels were significantly lower and seminal MDA levels were significantly higher in men with idiopathic infertility than in fertile men (P < 0.0001 and P = 0.004, respectively). A positive correlation was shown between sperm motility, sperm morphology, and TAC levels in men with idiopathic infertility (P = 0.002 and P = 0.002, respectively). In addition, there was a correlation between sperm motility and TAC levels in fertile men (P = 0.005). There was no correlation between sperm count and TAC levels in either men with idiopathic infertility or in fertile men. Negative correlations were observed between MDA levels and sperm motility, morphology, and sperm count only in men with idiopathic infertility (P = 0.003, P = 0.001, and P = 0.006, respectively). Conclusions: Our results show that oxidative stress could play an important role in male infertility as well as in sperm motility and sperm morphology.