Due to the environmental damage caused by synthetic materials such as plastic, there has been a growing interest in the development of new sustainable and biodegradable materials. Adenanthera pavonina L. is a plant species rich in galactomannan, a natural polysaccharide with the ability to form gels in aqueous solutions. Mauritia flexuosa L. (buriti) is a plant species rich in acids and oleaginous compounds, abundant in the Brazilian Amazon region. In this context, this work aimed to prepare galactomannan (Gal)-based films with mesocarp (MB) of the fruit of Mauritia flexuosa L., commonly called buriti, and characterize them by FTIR, XRD and density. Gal and MB were extracted from Adenanthera pavonina L. seeds and buritis, respectively. The films were prepared from 2% galactomannan + 0.5% MB solutions. FTIR spectra were obtained from the analysis of the samples in the spectral region of 600 to 4000 cm-1. The diffractograms were obtained using Cu Κα radiation (λ = 1.5418 Å) at intervals of 5° to 60° at room temperature, with an angular step of 0.02 and time of 2 s. The density of the films was calculated by the pycnometer method, using fractions of 1.5 cm × 1.5 cm of the samples. The FTIR spectra revealed characteristic absorptions of polysaccharides present in the galactomannan of Adenanthera pavonina L. and olefinic compounds and fatty acids present in the mesocarp of buriti. The diffractograms exhibited broad bands, indicating that the samples have an amorphous atomic structure. The measurements performed showed that the sample Gal2MB0.5 has a lower density than Gal2. From the results obtained, it is concluded that the Gal2MB0.5 sample has adequate physical and chemical properties to produce biodegradable plastics.