Wind turbine generators (WTG) used as alternative supply in a distribution system have different impacts on the system reliability performance than conventional alternative supplies due to the variable wind speed, This paper investigates the system reliability benefits of adding WTG as alternative supply in a rural distribution system, The wind generation interrupted energy benefit (WGIEB), the wind generation interruption cost benefit (WGICB), the equivalent number of conventional generators (ENCG) and the equivalent conventional generator capacity (ECGC) of one MW WTG are introduced. These indices provide direct reliability benefit indicators on the addition of WTG, and are important information for system planners to make planning decisions such as the selection of a wind site and the number of WTG, A test rural distribution system is utilized to illustrate the proposed technique. The effects on the system reliability benefits of the wind site selection and the number of wind units are investigated.