ABSTRACT The reason for conducting this review is to determine the effect of alkalization on the tensile strength and elasticity of composites of bamboo fiber and coconut fiber with a polyester matrix by varying the NaOH with concentrations of 0%, 2%, and 5%. Alkalization is one of the modifications of natural fibers to develop a compatible fiber-matrix. This exploration strategy uses the hand lay-up technique. In the main cycle, bamboo fiber and coconut fiber were treated without alkalization or 0% alkalization and in the next interaction, bamboo and coconut fiber were soaked in water (2% and 5% NaOH) for 2 hours. Then, at that time, each treatment process was formed into a composite according to the standard tensile test of ASTM D638 – II. The volume portion of bamboo fiber is 15%, coconut fiber is 15% and polyester resin is 70%, and the arrangement of bamboo fibers and coconut fibers is arranged horizontally. The matrix used in this study is a polyester resin matrix of type 157 BTQN with 1% MEKPO hardener. The highest concentration from this review showed that bamboo fiber and coconut fiber composites with NaOH variations of 0%, 2% and 5% respectively had tensile strengths of 34.9 MPa, 34.9 MPa and 54.74 MPa. The highest concentration with 5% NaOH produced the highest tensile strength of 54.74 MPa, while the coconut fiber composite without alkalization had the lowest tensile strength of 34.9 MPa.