The objective of this study was to determine the minimum sample size for studies of community structure and/or dominant species at different heights of a rocky intertidal zone at Rio de Janeiro. Community structure indicators suggested a variation in the minimum surface of 100 to 800 cm2, with a minimum of 2 to 8 profiles and at least 20 to 80 quadrant sampling points, depending on the height. Indicators of species abundance suggest 100 cm2 for Hypnea musciformis and 400 cm2 for Ulva fasciata, Phragmatopoma lapidosa Kinberg, (1867) and Gymnogongrus griffthsiae at lower heights; 200 cm2 for Chthamalus spp. at intermediate heights; and 800 cm2 for Littorina ziczac at the greatest height. In general, seven to eight profiles and 10 to 20 sampling points were used. Different sample sizes were related to the abundance and spatial distributions of individual species, which varied at each intertidal height according to the degree of environmental stress.The objective of this study was to determine the minimum sample size for studies of community structure and/or dominant species at different heights of a rocky intertidal zone at Rio de Janeiro.Community structure indicators suggested a variation in the minimum surface of 100 to 800 cm2, with a minimum of 2 to 8 profiles and at least 20 to 80 quadrant sampling points, depending on the height. Indicators of species abundance suggest 100 cm2 for Hypnea musciformis and 400 cm2 for Ulva fasciata, Phragmatopoma lapidosa Kinberg, (1867) and Gymnogongrus griffthsiae at lower heights; 200 cm2 for Chthamalus spp. at intermediate heights; and 800 cm2 for Littorina ziczac at the greatest height. In general, seven to eight profiles and 10 to 20 sampling points were used. Different sample sizes were related to theabundance and spatial distributions of individual species, which varied at each intertidal height according to the degree of environmental stress.