To determine the main diatom taxa found in the natural diet of Haliotis fulgens Philippi (green abalone) and H. corrugata Wood (pink abalone) juvenile specimens and loose rocks were collected from different depths at two sites in Bahía Tortugas and Bahía Asunción, Baja California Sur. Overall 113 benthic diatom species were identified, and 98 taxa were recorded in the gut contents of both abalone species. Out of these 32 were not observed in the surrounding flora. Most diatom taxa were epiphytic forms, including the abundant taxa found in the gut contents of young abalone: Berkeleya fennica, Cocconeis speciosa, Cocconeis costata var. pacifica, Gomphonemopsis pseudexigua, Grammatophora marina, Navicula parva, Tabularia investiens, and Thalassionema nitzschioides. This somewhat re-flected the structure of the diatom assemblages in the rocky habitat: few abundant taxa and many rare or uncommon ones, with heterogeneous values of diversity (H') that ranged between 1.1 and 4.2 in the gut contents and from 2.83 to 3.91 in the surrounding flora. New records for the area include Cocconeis pseudomarginata, C. maxima (common), Licmosoma sp., Ardissonia formosa (rare), and the colonial form Berkeleya fennica (abundant), all found within the gut contents of abalone. The actual and potential diet of young abalone on the coast of Baja California Sur is extended to 235 taxa. The abundant taxa occurred frequently in clumps of numerous individuals in the gut contents, often still attached to algal tissue. The results of this investigation suggest that the importance of diatoms in the diet of larger juvenile abalone merits reassessment.