The female reproductive system of Omorgus suberosus (Fabricius) is described and reproductive states identified and characterized based on the length of the basal oocytes. Using regression tree analysis, three groups were identified: immature females (≤1.29 mm), maturing females (1.30–2.06 mm), and mature females (≥2.07 mm), and differences in basal oocyte length were found among states of maturity. This study provides basic information for future studies on the ecology and reproductive behavior of O. suberosus, useful to understand the population dynamics of this species.