Due to the susceptibility of ether bonds to oxidative radicals, the synthesis of ether-free polymer electrolytes has been undertaken to create chemically stable proton exchange membranes suitable for long-lasting fuel cell applications. Herein, we present a series of ether-free sulfonated poly(fluorenyl biphenyl indole) (SPFBI) obtained through a feasible and cost-effective process. Thanks to the ether-free structure, SPFBI membranes demonstrate high chemical stability and proton conductivity, reaching up to 0.1956 S cm-1 at 80°C. During the open circuit voltage stability test, the membrane electrode assemblies utilizing the SPFBI-0.2 membrane endured over 620 hours without significant defects. As a result, this study offers a remarkable approach for optimizing ether-free hydrocarbon-based polymer structures, making them highly suitable for both polymer electrolyte membrane applications, showcasing excellent proton conductivity and chemical stability.