Natural fiber-reinforced composites are currently used for various types of applications. However, to improve the fiber/resin bonding at the interface, some suitable chemical modification of the fibers is required. In the present study, an attempt has been made to use an inexpensive, easily available, and water-soluble (in alkaline medium) natural resin shellac for the surface treatment of jute yarns. Jute yarns were treated with 1%, 2%, and 5% shellac solution, and these treated jute yarns were used as reinforcing material in vinylester resin matrix composites. The composites were subjected to flexural tests, and the flexural properties were found to be highest in the case of 1% treated composites. A dynamic mechanical study also showed the same trend, and the storage modulus was found to be highest for the 1% treated composites at room temperature. The fractured surfaces of the composites, as observed by SEM, were correlated with the mechanical properties.