The optical properties of aerosols from biomass burning in Brazil were derived from measurements by the AERONET sun photometer network in Amazonia. A dynamical aerosol model was constructed from Mie Theory calculations, using as input a constant complex refractive index and the average size distribution of aerosols for 12 ranges of aerosol optical thickness. The aerosol optical properties were described for 24 wavelengths in the spectral range of 0.20--3.00 ¿m. The model was used to simulate radiances and irradiances and the results agreed well with the measurements. The derived optical model is immediately applicable to estimate aerosol forcing by biomass burning aerosol emitted on the development frontier in Amazonia.