A Mobile Ad-hoc Network (MANET) is a group of active mobile nodes wirelessly connected in a self-configuring and self-healing network without a preexisting centralized infrastructure. Several studies have been conducted to improve the stability and lifetime of routes for communicating between source and destination nodes, integrating new techniques with existing protocols. This paper presents a fuzzy-based approach to improve the performance of the standard Zone Routing Protocol (ZRP) by selecting the optimal value of the zone radius. Each node has a fuzzy inference system that is periodically fed with parameters, such as the remaining energy and mobility of the node, to calculate the optimal value of the zone routing radius, which makes the node autonomous and intelligent. The simulation results obtained using the NS-2 simulator showed that the proposed fuzzy radius approach outperformed the standard ZRP, OVBAZRP, and PSOZRP routing protocols in all measures considered: PDR, NRL, and E2ED.