Soldiers and workers are non-reproductive castes in the termite, Reticulitermes aculabialis Tsai et Hwang. Soldiers develop from workers.We used a histological dyeing method to observe the oogenesis of soldiers and workers and to explore the difference in gonad development between these castes and the reason for the soldiers’ sterility.The results show that gonad size was significantly different in these two castes (P＜0.01) and that the sectional area of workers’ ovaries was 7 times that of soldiers.Compared with workers,there was only a differentiation stage in oogenesis in soldiers and no growth stage.Soldiers’ oocytes were significantly smaller than those of workers at the differentiation stage; the volume ratio (soldier:worker) being 1∶16.These results prove that further degradation of the ovary occurs as workers become soldiers causing soldiers to lose their potential reproductive ability.Our results provide histological evidence for soldiers’ sterility,and also show that there is a histological basis for the difference in potential reproductive capacity between soldiers and workers.