Phospholipid hydroperoxide glutathione peroxidase (PHGPx) is known to be an antioxidant enzyme that may be implicated in spermatogenesis, but its functional significance in the development of testes remains poorly understood. To demonstrate the roles of PHGPx in spermatogenesis during postnatal development, expression profiles of PHGPx mRNA and protein in testes and epididymides obtained from mice 1-9 and 27 weeks after birth were spatiotemporally analyzed. In testes, PHGPx mRNA first appeared in 2-week-old mice, while its protein was first detected in late spermatocytes and round spermatids from 3-week-old mice and levels were greatly increased in elongated spermatids and immature spermatozoa of 5-week-old mice. These increased levels were maintained until 27 weeks as well as weak expression in Leydig cells. In the epididymides, PHGPx mRNA was weakly detected in all ages examined, while PHGPx protein first appeared at 4 weeks, greatly increased after 6 weeks, and was observed strongly in luminal sperm and weakly in surrounding tubular epithelium until 27 weeks. These findings indicate that PHGPx is essential for postnatal spermatogenic activity in mice.