In this research work, the Phoenix sp . fiber‐based epoxy composites were fabricated using compression molding technique and investigated their mechanical and free vibration characteristics by varying the fiber length and content. The test results indicated that the fiber length and content influence the properties of composites significantly. The composites showed higher mechanical and free vibration properties than the neat epoxy due to increased composite stiffness. In particular, the composites reinforced with 20 wt% of 15 mm length fiber offer better overall properties. In addition, an effort was made to improve the properties of the optimized composites by reinforcing the sodium bicarbonate treated Phoenix sp . fibers. The treatments showed a positive impact on the composite properties, especially the 120 h treated fiber reinforced composites offered highest mechanical and free vibration properties than the other composites investigated. This could be attributed to increased fiber‐matrix interfacial bonding and the existence of small protrusions on the fiber surface that act as a mechanical interlocking mechanism, and the same was confirmed through morphological analysis. The experimental results showed that the sodium bicarbonate treatment is efficient in increasing the properties of Phoenix sp . fiber composites, as well as being less harmful to the environment after disposal.