We studied the effects of sex, body size, and season on the diet of two populations of the Blue-Bellied Poison Frog Andinobates minutus (Anura: Dendrobatidae) along the Pacific coast of Colombia. Andinobates minutus had a specialist diet, with preference for Acari (mites), Formicidae (ants), Collembola (springtails), and Holometabolous larvae. No differences in diet composition were noted between populations or between seasons. However, prey volume was higher in frogs from Bahía Málaga than those from Isla La Palma, and both populations experienced a decrease in the number of prey items in November, caused possibly by the low prey availability in that month. A differential effect of body size on diet was noted between populations. The total volume of prey, the volume and number of ants, and the volume of mites increased with snout–vent length (SVL), whereas the number of springtails decreased with SVL only in the Bahía Málaga population but not in the Isla La Palma population. This differential effect could be caused by the difference in distributions of the individuals' body sizes between populations. A significant effect of sex on diet was noted in both populations. Females from both populations showed higher preference for ants than did males. However, the importance of Formicidae showed temporal fluctuations in both populations. The diet of A. minutus in both populations had an important phylogenetic component, because closely related species have similar diets. Although other factors affected diet, the differential effects observed between populations could be caused by the spatiotemporal dynamic of each population.