Miwi, a member of the Argonaute family, is required for initiating spermiogenesis, however, the mechanisms that regulate the expression of the Miwi gene remain unknown.By mutation analysis and transgenic models, we identified a 303 bp proximal promoter region of the mouse Miwi gene, which controls specific expression from midpachytene spermatocytes to round spermatids during meiosis.