Aim: To investigate the association of glutathione S-transferase T1 (GSTT1) gene polymorphism in patients with idiopathic azoospermia or oligospermia in the northwestern China population. Methods: In the case-control study, GSTT1 genotypes were identified by multiplex polymerase chain reaction (PCR) with peripheral blood DNA samples from 78 patients with idiopathic azoospermia, 103 patients with idiopathic oligospermia and 156 age-matched controls with normal sperm concentration and motility, according to the criteria adapted from World Health Organization guidelines. All of the patients and controls were from northwestern China. Results: There is a significant association between GSTT1 null genotype with idiopathic azoospermia risk (odds ratio [OR]: 2.36, 95% confidence interval [CI]:1.33-4.20, P = 0.003) or idiopathic oligospermia risk (OR: 2.00, 95% CI: 1.17-3.27, P = 0.010). Conclusion:GSTT1 null genotype is a predisposing risk factor for sporadic idiopathic azoospermia or oligospermia in north-western China.