The West Indian sweetpotato weevil Euscepes postfasciatus (Fairmaire) (Coleoptera: Curculionidae) is a major pest of sweetpotato Ipomoea batatas (L.) Lam (Solanales: Convolvulaceae) in some countries. In order to improve mass-rearing for an eradication program employing the sterile insect technique (SIT), optimal population density of E. postfasciatus in an artificial diet was examined. Six population densities (1000, 4000, 7000, 10000, 13000, and 16000 individuals per container with 200 g of artificial diet) were compared for effect on the number of eggs collected and hatchability. The total number of eggs collected after 24 d increased with an increase in population density and reached a saturation level at 13,000 individuals, whereas hatchability was not affected by population density. The results indicated that optimal population density in mass rearing was 13,000 individuals on 200 g of artificial diet. Furthermore, we examined cannibalism by adult weevils in the presence of other diets. The result suggested that egg cannibalism may be a major reason for the low rate of egg collection in the mass rearing of E. postfasciatus.