Resumo. ABSTRACTThe study was made in Atlantic forest fragments in the lowland region of the protected area of São João riverbasin, Rio de Janeiro state, Brazil. The aim of the study was to test the hypothesis that fragment size altersmacro-nutrients concentrations in leaves of the main tree species (Guarea guidoneaeCupania oblongifolia)in the area. Adult leaves ofGuareaeCupaniawere sampled in three small (23- 33 ha), three medium(130 - 155 ha) and three large (500 - 2300 ha) fragments. Carbon, N, Ca, Mg and K were determined.The results showed that, in general, the reduction of the fragment size did not affect the nutritional statusof the species studied. Nevertheless, the higher Mg concentrations inCupania oblongifolialeaves in thesmall fragments (5.0±0.8 mg/g) compared with the medium (4.0±0.3 mg/g) and large (3.5±0.7 mg/g) onesindicated an effect of the reduction of the fragment area over this element.