In this study, nanocomposites based on unsaturated polyester cured by ultra-violet (UV) radiation were prepared using Kenaf bast fibre and Montmorillonite (MMT) as reinforcing agent at different percentages. MMT was modified using an ion exchange process by replacing the sodium ions with alkyl ammonium ions from Cetyltrimethylammonium Bromide (CTAB). From the results obtained, the microstructure of MMT modified with CTAB (MMT-CTAB) showed the interlayer spacing of MMT-CTAB was increased and X-ray diffraction analysis indicated that cation exchange between CTAB and MMT was evident. As for the composites prepared from untreated MMT-CTAB, it showed higher mechanical properties as compared to those prepared from untreated MMT. On the other hand, the percentage of Kenaf fiber in the nanocomposites system also plays a crucial role in determining the nanocamposites properties.