Background Infertility is a major medical and social problem, and elementary research on the spermatozoal proteins and their functions are relatively scarce and there are very few confirmed and effective options for the treatment of male infertility. Thus, it is essential to find candidate proteins that affect male infertility. This study was designed to detect the proteins with differential expression in sperm from infertile patients and normal donors.Methods Semen samples from patients with idiopathic asthenozoospermia (n=114) and from fertile men with normal spermiograms (n=37) were collected. Semen sample analysis, sperm protein extraction, SDS-PAGE electrophoresis and Western blotting analysis were performed. Results were analyzed by SPSS 16.0 statistical software.Results Western blotting analysis of spermatic proteins displayed a major differentially expressed protein in spermatozoa from fertile and idiopathic asthenozoospermia patients. Densities and volumes of the identified protein in the patients were significantly decreased compared to normal donors (P=0.034 and P=0.036, respectively). The protein was identified as DEAD-box protein 4 (DDX4, VASA). The expression and correction value (CV) of DDX4/VASA in the patients was reduced significantly compared to normal donors (P=0.037 and P=0.031, respectively).Conclusions The expression of spermatic protein DDX4/VASA associates with spermatic motility, implying that DDX4NASA may be a candidate marker for evaluation of spermatic motility.