Previous study on Cancer setosus Molina, 1782 showed that latitudinal changes in temperature control the number of annual egg masses. This study focused on the effects of preoviposition temperature and female size on egg traits in C. setosus from northern (Antofagasta, 23° S) and central-southern (Puerto Montt, 41°S) Chile. Blastula eggs produced in nature ranged in dry mass (DM) from 9.1 to 15.1 μg, in carbon (C) from 4.8 to 8.4 μg, in nitrogen (N) from 1.0 to 1.6 μg, in C:N ratio between 4.7 and 5.4, and in volume (V) between 152 and 276 mm3 × 104 per female. Blastula eggs from females caught early in the reproductive season in Puerto Montt (September 2006) were significantly higher in DM, C, N, and V than those of females caught 2 mo later, reflecting a seasonal increase in water temperature. In Puerto Montt early and late season blastula eggs were higher in DM, C, N, and V than eggs from Antofagasta by about 32 and 20%, respectively. Subsequent egg masses produced in captivity in Puerto Montt followed this pattern of smaller eggs with lower DM, C, and N content at higher pre-oviposition temperatures. In Antofagasta no significant difference in DM, C, N, and V between eggs produced in nature and subsequent eggs produced in captivity was found and all egg traits were significantly positively affected by maternal size. Reproductive plasticity in C. setosus helps to explain the species wide latitudinal distribution range.