In an experimental site for reforestation of degraded area, three-year-old plants of Bertholletia excelsa Humb. & Bonpl. were subjected to different fertilization treatments: T0 = unfertilized control, T1 = green fertilization (branches and leaves) and T2 = chemical fertilization. Higher net photosynthetic rates (PN) were observed in T1 [13.2±1.0 μmol(CO2) m-2 s-1] compared to T2 [8.0±1.8 μmol(CO2) m-2 s-1] and T0 [4.8±1.3 μmol(CO2) m-2 s-1]. Stomatal conductance (g s), transpiration rate (E) and water use efficiency (WUE) of individuals of T1 and T2 did not differ significantly, however, they were by 88, 55 and 63%, respectively, higher in T1 than in the control. The mean values of variable fluorescence (Fv), performance index (P.I.) and total chlorophyll [Chl (a+b)] were higher in T1. Our results indicate that green fertilization improves photosynthetic structure and function in plants of B. excelsa in young phase. and M. J. Ferreira, J. F. C. Gonçalves, J. B. S. Ferraz.