Sublethal doses of chlorfluazuron (LD₁₀: 1.00 ng per larva or LD₃₀: 3.75 ng per larva) topically applied on newly molted fifth instars of Spodoptera litura (F.) significantly reduced ovarian weight and number of mature eggs in pupae and adults, compared with those of the controls. The ratios of fresh ovarian/fresh body weight, dry ovarian/fresh ovarian weight, and dry ovarian/fresh body weight were the same among controls, LD₁₀, and LD₃₀treated newly emerged adults. In treated adults, the germarium was significantly longer than the pedicle and vitelarium compared with those of the controls, whereas in controls the vitelarium was significantly longer than the germarium and pedicle. This indicates a delayed of maturation of ovarioles in treated cutworms. These doses also disrupt growth and development of oocytes by significantly affecting the size of basal oocytes and thickness of follicular epithelium. The maximum size of basal oocytes recorded on the day of adult emergence was significantly reduced in LD₁₀or LD₃₀treated females, compared with those of the controls. The thickness of the follicular epithelium of basal oocytes reached to a maximum in the controls on the eighth d and in treated females on the ninth d after pupation. In newly emerged treated adults, the protein content of ovaries was significantly reduced but the carbohydrate and lipid contents were not significantly affected, compared with those of the controls. The effects of chlorfluazuron on ovarian development and oogenesis are presumed to be responsible for the reduction in fecundity caused by sublethal exposure to chlorfluazuron.