This study summarizes the research on organic fillers, where eggshells were used as the reinforcement and banana peels as the matrix in the manufacturing of biocomposite thin film. Banana peel fibers exhibit a good characteristic of renewable material for the substitution of cement-based composites. However, biocomposite properties are limited by the poor adhesion between natural fiber interface and polymer matrix, which can be improved by chemical modification of fibers. In this research, banana peels were subjected to silane treatment. Biocomposite thin film manufacturing processes were carried out using blending and hand lay-up techniques with various concentrations of epoxy/waste banana peels/eggshell filler (EWE) ratios (EWE 0%, EWE 5%, and EWE 10%). X-ray diffraction (XRD), Fourier transform infrared (FTIR), thermogravimetric analysis (TGA), and thickness swelling test were conducted on silane-treated and untreated banana peel biocomposite samples. In XRD analysis, it was found that EWE 10% sample had the highest crystallinity compared to EWE 0% and EWE 5%, and silane-treated samples had higher crystallinity than untreated samples. For FTIR test, lignin component was removed in silane treatment based on the changes of IR peak characteristic where the new bonds (-Si-O-C-, -Si-O-Si-, and -Si-C-) were found in treated samples. Besides, TGA results showed that the thermal stability of silane-treated samples was improved significantly with the increase of eggshell filler percentage, which was proven by the decrease in the decomposition stage. In thickness swelling test, the samples achieved higher swelling percentage as the percentage of eggshell filler increased. However, the decrease of 5–6% in thickness swelling of treated samples was possibly offset by the enhancement in fiber/matrix interfacial adhesion.