This study aimed to determine the effect of the long soaking of coir in sodium hydroxide solution on its mechanical properties. The materials used, namely coir, sodium hydroxide solution, polyester matrix, catalyst, and aquades. The coir was soaked in a sodium hydroxide solution for 1, 5, 7, 9, and 11 hours. After that, coconut fibre was washed using distilled water, and then dried in an oven at 90 °C for 5 hours. Next, a single fibre tensile and pull out test was performed. Based on the results and discussion, it was concluded that immersing coconut fibre in sodium hydroxide solution for 7-hours gave the maximum tensile strength and interfacial shear strength of 223.91 N/mm2, and 9.8 N/mm2, respectively Coir as a composite reinforcement has the potential to be used for engineering material such as ceiling boards and fishing boat walls.