In this study, biodegradable composites were prepared which were reinforced with pineapple fiber and fillers (coconut, eggshell and seashell) epoxy polymer resin. All prepared bio composite samples were characterized for thermal characteristics using thermogravimetric analysis (TGA) and chemical composition of fabricated samples were investigated using Fourier Transform Infrared Spectroscopy (FTIR). The study was focused on the effect of reinforced fillers on the thermal stability of prepared composites and their identification for absorbance peaks in FTIR analysis. Results of TGA show that all prepared composite exhibits the glass transition temperature between 250 and 275 °C. Pineapple/epoxy/seashell presents higher amount of residue as compared to pineapple/epoxy/coconut and pineapple/epoxy/eggshell composites. FTIR results revealed the presence of hydroxyl group and creation of hydrogen bonding by absorbance peaks between 3500 and 3900 cm−1 wavenumber. Absorbance peaks between 500 and 1500 cm−1 wavenumber proves the amount of cellulose, lignin and pectin in prepared composite specimens.