From the CH2Cl2 extract of the temperate marine red alga, Laurencia rigida, which has antifouling properties, eight sesquiterpenes (1-8) were isolated. Of these, four (3-acetoxy-E-gamma-bisabolene (1), (-)-10 alpha-bromo-9 beta-hydroxy-alpha-chamigrene (2), rigidol (3), and (+)-(10S)-10-bromo-beta-chamigrene (4)), were shown to be new natural products. For the known compound deschloroelatol (5), reassignment of the 1H- and 13C-NMR data was found to be necessary on the basis of extensive NMR measurements. For elatol (6), complete 1H- and 13C-NMR data are also reported. The antimicrobial and antialgal activities of all isolates were assessed.