JMJD1A (jumonji domain-containing 1A), a known histone H3K9 demethylase, has been identified as a critical epigenetic regulator in male germ cells, activating the sperm chromatin-packaging genes encoding protamines (PRM) and transition proteins (TNP) required for spermatid elongation and condensation. This research investigated the expression pattern of JMJD1A protein in testicular biopsies of 79 infertile men who had undergone testicular sperm extraction. Samples were classified into obstructive azoospermia (OA, n = 26), round spermatid maturation arrest (SMA, n = 29) and Sertoli cell only syndrome (SCOS, n = 24). Experiments including the detection of mRNA and protein expressions of JMJD1A revealed a severe decrease of JMJD1A/JMJD1A in samples with SMA and SCOS compared with samples with OA (P < 0.005, Kruskal−Wallis test). Additional experiments, including incorporation of JMJD1A on the promoter regions of TNP and PRM genes, and the expression of these genes, showed a significant decrease in the SMA and SCOS versus the OA testes (P < 0.005, Kruskal-Wallis test). These findings show the low expression of JMJD1A/JMJD1A, as well as its low incorporation into chromatin in testes with round spermatid maturation arrest, suggesting that a deficient expression of JMJD1A/JMJD1A might be reflecting and/or contributing to round spermatid maturation arrest.