Bioassay-guided fractionation of the MeOH extract of the leaves of Grevillea robusta led to the isolation of six new 5-alkylresorcinols, gravicycle (1), dehydrogravicycle (2), bisgravillol (3), dehydrobisgravillol (4), dehydrograviphane (5), and methyldehydrograviphane (6), as well as eight known compounds. The structures of these compounds were determined by spectroscopic and chemical methods. Graviphane (7) and methylgraviphane (8) were isolated in the pure form for the first time from a natural source. The compounds all showed marginal cytotoxicity against MCF-7, NCI-H460, and SF-268 cell lines.