The diet of the Cape Petrel was investigated in two localities of South Shetland Islands, Antarctica, over the period January—February 1996. Stomach contents of adults obtained by flushing and regurgitates of chicks were sampled during the chick-rearing period. During the whole sampling period, euphausiids represented the predominant prey in terms of frequency of occurrence, mass and number at Fildes Peninsula, while at Harmony Point, euphausiids and fish components were found in similar proportions in terms of mass and frequency. Myctophiids fish, in particular Electrona antarctica, formed the bulk of the fish component. The analysis of the diet throughout the breeding season showed significant differences in number and mass of the prey items at Fildes Peninsula, while at Harmony Point, there were significant differences also in the occurrence of preys. Considering both localities, although the occurrence of the prey did not vary significantly during the brooding period, there were significant differences in their number and mass. Similar results were found in the post-brooding period between both localities.