The interest in natural reinforced polymer composite materials is rapidly growing both in industrial and basic research applications. This is based on its availability, renewability, low density, cheapness, biodegradability, and satisfactory mechanical properties. The research reports on the isolation and characterization of cellulose from Pentaclethra macrophylla Benth Pod (PMBP) biomass wastes for polymer reinforcement composites. Cellulose was successfully isolated from PMBP biomass via delignification and bleaching. X-ray diffraction (XRD), scanning electron microscopy (SEM), Fourier Transform Infrared Spectrometry (FTIR), thermal gravimetric analysis (TGA), and deformation gravimetric analysis (DGA) were used to characterise the raw and isolated cellulose. The isolated cellulose has better thermal stability, crystallinity, and porosity than the raw cellulose. The removal of the matrix material (most hemicelluloses and almost all the lignin) led to an increase in the crystallinity and the maintenance of the thermal stability of the cellulose. The functional group elucidation showed that both raw and isolated contained cellulose, the morphology of the cellulose revealed some essential elements that are suitable for good polymer reinforcement composites. The obtained cellulose could serve as a reinforcing material in composite products or as a raw material for other applications.