Most small rodent species display cyclic fluctuations in their population density. The mechanisms behind these cyclical variations are not yet clearly understood. Density-dependent effects on reproductive function could affect these population variations. The fossorial water vole ecotype, Arvicola terrestris, undergoes a multi-year cycle dynamic with outbreak peaks. Here, we monitored different water vole populations over three years, in spring and autumn, to evaluate whether population density be related to male reproductive physiology. Our results show an effect of season and inter-annual factors in testes mass, plasmatic testosterone level, and androgen-dependent seminal vesicles mass. By contrast, population density does not affect any of these parameters, thus suggesting a lack of modulation of population dynamics of population density.