The cytological study of males and females of Trichuris muris (Schrank, 1788) revealed the diploid number of chromosomes to be 2n = 6. The sex determining mechanism was XX female/XY male. All the chromosomes were subtelocentric. Sex chromosomes formed the smallest pair, but X and Y were difficult to distinguish morphologically. Chromosome changes during gametogenesis in both sexes followed a classical pattern except in the male prophase and metaphase I. Four male autosomes formed two bivalents, each with one proximal chiasma with strict localization, while sex chromosomes X and Y formed two univalents. Female chromosomes formed three rod bivalents of normal type, which possessed three, two and two chiasmata.