Natural fibers have shown promise as reinforcement in polymer matrix composites in automotive applications. Due to the presence of hydroxyl groups from cellulose and lignin, natural fibers exhibit highly hydrophilic properties. This makes fiber-matrix adhesion very difficult because most structural polymers are hydrophobic in nature. Therefore, in order to maximize natural fiber reinforced composite performance, fiber surface modification is required. In addition, a chemical additive to polymer matrix is another direction to improve the performance. In this study, several types of natural fibers were chosen, including European flax fiber, North American flax, and North American hemp fiber. Sodium hydroxide treatment followed by acrylic resin treatment was investigated for its influence on vinyl ester cure kinetics and interfacial properties.