Female bees need to develop their ovaries for oviposition, and it has been considered that the pollen nutrition would be important for ovarian development. However, few studies empirically examined the relationship between pollen intake and ovarian development. In the present study, we investigated the effect of pollen diet on ovarian development of female bees, using workers of Japanese bumblebee, Bombus ignitus (Smith). We reared newly emerged workers in two different diet conditions: (1) both pollen and nectar and (2) nectar only. We dissected the ovaries and ranked their development on day 0, 7 or 14 after emergence. In addition, to clarify whether pollen intake affects the status of ovarian development, we confirmed the presence or absence of pollen in the digestive tract. The stage of ovarian development was affected by treatments and number of days since emergence. The ovaries of workers that fed on pollen and nectar developed more than that fed on nectar only. Moreover, the ovaries of workers with pollen in the digestive tract developed more than those of workers without pollen. Our results demonstrated the importance of pollen feeding for promoting ovarian development of bumblebee workers.