The bare-tailed woolly opossum, Caluromys philander, and the kinkajou, Potos flavus, are two syntopic neotropical nocturnal, arboreal and frugivorous mammals. Because of close ecology but great difference in size (weight 300 vs 3000 g), they represent pertinent models to examine the influence of size on foraging strategy. These species were studied by radio-tracking and direct observation during 22 months in a tropical forest in French Guiana. Both mammals’ foraging strategies with regard to flowers and fruits are characterized as follows: (1) numerous plant families and species are exploited; (2) most plant species are selected according to their abundance; (3) diet selectivity and diversity are similar in both mammals; (4) relative parts of flowers and fruits in the diet vary according to their year-long availability; (5) the choice of fruiting species is not related to the morphological type, size, or nutritious quality of fruits but instead depends on easy access to the edible part; (6) the length of foraging bouts is correlated with production for the most frequently exploited tree species; (7) feeding bouts are shorter in P. flavus than in C. philander; (8) P. flavus exploits large, highly productive canopy trees, while C. philander also visits canopy trees with low production and understorey trees. In conclusion, both mammals are opportunistic flower- and fruit-eaters, but the larger species (P. flavus) exploits larger, more scattered food patches, while the smaller one (C. philander) also exploits smaller, more numerous and more evenly distributed food patches.