Coconut coir rope has emerged as a promising sustainable reinforcement for cementitious composites; however, its durability under aggressive chemical environments remains a critical concern. This study investigates the mechanical degradation of coconut coir rope exposed to saline (NaCl) and alkaline (NaOH) environments at concentrations of 2%, 5%, and 8% for immersion periods of 3, 7, 14, and 30 days. Following exposure, uniaxial tensile tests were performed to evaluate atensile strength, and apparent modulus. The results indicate that NaCl exposure causes only minor variations in tensile strength and stiffness, with no statistically significant dependence on concentration or immersion time. In contrast, NaOH treatment produces pronounced and nonlinear changes in both tensile strength and apparent modulus. Moderate alkaline exposure improves mechanical performance due to surface cleaning and enhanced inter-fiber bonding, while prolonged or high-concentration NaOH leads to cellulose degradation, fiber swelling, and loss of structural integrity. Response surface methodology (RSM) was employed to develop predictive models for tensile strength and apparent modulus using NaCL/NaOH concentration, immersion time, and relevant physical parameters. The models exhibited strong predictive capability, with coefficients of determination of approximately 0.861 0.95 for NaCL and NaOH treatment respectivelly, indicating excellent agreement between experimental and predicted results. The developed experimental–modeling framework provides a reliable tool for predicting the durability of coconut coir rope both in saline and alkaline cementitious environments and supports its application as an eco-friendly reinforcement material.