RING finger proteins play important roles in spermatogenesis. Here, we report that a novel RING finger protein RNF151, with a C3HC4-type RING finger domain, a putative nuclear localization signal (NLS), and a TRAF-type zinc finger domain, was exclusively expressed in the mouse testis and developmentally regulated during spermatogenesis. While RNF151 mRNA was present in round spermatids, its protein was expressed in elongating spermatids of the stage VIII-IX seminiferous tubules. The NLS together with the RING domain were necessary and sufficient for the nuclear localization of RNF151-EGFP in transfected cells. Yeast two-hybrid screening identified the physical interaction of mouse RNF151 and dysbindin, which was confirmed by the co-immunoprecipitation of the proteins and by their co-localization in intact cells. As dysbindin has lately been shown to be involved in membrane biogenesis and fusion, a key process for acrosome formation, we propose that RNF151 may play a role in acrosome formation.