Within humans sperm are exposed to high concentrations of a single CRISP during epididymal maturation (called CRISP1). By contrast mice are exposed to two CRISPs, CRISP1 and CRISP4, thus raising the hypothesis that human CRISP1 function is equivalent to the combined actions of CRISP1 and CRISP4 in the mouse. In order to explore this hypothesis and to define the role of CRISPs in epididymal sperm maturation, we produced homozygous Crisp1 knockout mice and cross-bred them with homozygous Crisp4 knockout mice to generate homozygous Crisp1-Crisp4 double knockout mice. Double knockout mice produce normal litter sizes compared to wild type litter mates, however, their sperm show functional deficits. Sperm were collected from mature male mice cauda epdididymides via the back flushing method and analyzed by using a computer-assisted sperm analyzer (CASA). CASA data showed that sperm from double knockout mice had significantly decreased total motility compared to that of wild type (wt) mice (74.75% vs. 83.50% respectively, p<0.01). Further, progressive sperm motility also significantly decreased (p<0.01) between double knockout mice (39.63%) and wt mice (55.75%). We also analyzed sperm parameters of Crisp4 single knockout mice, however, no significant difference was found between wt and Crisp4 knockout mice in terms of sperm motility and progressive sperm ratio. Our preliminary results have demonstrated that CRISPs function during epididymal sperm maturation in order to obtain optimal sperm function and thus fertility.