The present study evaluated the association between offspring sex ratio and parental inherited variations of xenobiotic metabolism by glutathione S-transferase (GST) T1 and GSTM1. Polymorphisms of GSTT1 and GSTM1 were investigated in 235 Iranian Muslims (153 males, 82 females) using polymerase chain reaction-based method. Statistical analysis of 890 offspring in the study families revealed that there was no association between GSTM1 null genotype of either the fathers (OR=1.28; 95% CI=0.88-1.85; P=0.17) or mothers (OR=0.77; 95% CI=0.49-1.19; P=0.22) and offspring sex ratio. There was no association between paternal GSTT1 null genotype and sex ratio in offspring (OR=1.04; 95% CI=0.71-1.54; P=0.84), whereas there was a weak association between maternal GSTT1 null genotype and offspring sex ratio (OR=1.54; 95% CI=1.0-2.38; P=0.05). Combination of parental GSTT1 and GSTM1 genotypes showed no association with offspring sex ratio.