Vibration and fatigue study of glass-reinforced nylon, as an alternative material to steel for engine driven fans, is discussed. The use of nylon, which has a lower density than steel, offers a significant weight reduction and consequently less burden on the related underhood components and result in longer life for water pumps, fan clutches and drive belts. The temperature and humidity-dependent properties of nylon fan often works favorably from the view point of fatigue life, by shifting the fan's natural frequencies away from the occurrence of resonance. Nylon fans also offer more design flexibility without significantly affecting the cost.Despite such apparent advantages very little literature in the automotive field has dealt with vibration and fatigue of nylon fans. In this paper, computer-based finite element method (FEA) is used as the analytical tool to determine the frequencies and stresses produced at different values of temperature, humidity, and vibration excitations. Comparisions were made against experimentally obtained data, and have seen good agreements. Fatigue analysis was also conducted in order to predict life-expectancy of the nylon fans.