The trophic ecology of two dominant intertidal caprellids, Caprella penantis and Caprella grandimana, was studied by examining gut contents. Samples were collected from Tarifa Island (Punta Marroqui, 36°00′00.7″N 5°36′37.5″W) bimonthly from December 2005 to December 2006 to explore seasonal and sex-related differences in diet. The gut contents of the two species included detritus, metazoan prey (crustaceans, polychaetes, hydroids, nematodes, and turbellarians), macroalgae, microalgae, and dinoflagellates. The dominant component was detritus, followed by crustaceans, mainly copepods, and macroalgal tissues. A three-way analysis of variance was conducted using the factors “species” (C. penantis vs. C. grandimana), “sex” (males vs. females), and “month” (seven dates, December 2005–December 2006). Males of both species had a significantly higher proportion of prey and a lower proportion of detritus in their guts than females. The larger body and gnathopod 2 of males appeared to be related to a more carnivorous diet. Both species fed more on crustaceans and macroalgae during the summer (April, June, and August), probably owing to fluctuations in prey availability and seasonal variations in algal abundance. Moreover, C. penantis was significantly more predatory than C. grandimana, but both species had a diet based mainly on detritus and crustaceans. Caprella penantis dwells at the lower intertidal and C. grandimana at the mid-tide level, which may reduce competition between the species.