This study evaluated the effect of different diets on the feeding, growth, and proximal composition of Octopus mimus. Animals were kept under controlled conditions in the laboratory for 3 mo and fed ad libitum with monodiets of the molluscs Eurhomalea lenticularis and Tagelus dombeii, and the crustacean Mursia gaudichaudi. The specific feeding rates (SFRs) of O. mimus were significantly greater in individuals fed with M. gaudichaudi (1.70% body weight per day), whereas the greatest specific growth rates (SGRs) were obtained in individuals fed with T. dombeii (0.26% body weight per day) and E. lenticularis (0.15% body weight per day). The weight increase of O. mimus was affected by the treatments, and the greatest increase throughout the duration of the experiment was observed in octopuses fed with E. lenticularis (0.12% per individual). Although the gender of the animals did not directly influence SFR and SGR, males had a greater weight increase, probably because some females laid eggs during the experimental period. The quantity of macronutrients in the different treatments was not clearly reflected in the growth parameters of O. mimus, because a high protein content (i.e., M. gaudichaudi) did not necessarily give a greater growth rate or a greater weight increase. It is necessary to consider the quality of each of the dietary components, because the changes observed in the tissue composition of O. mimus are related to the feeding levels and variability in growth.