This paper deal with an analysis of impact of climate conditions on field reliability of vehicles. Two case studies are presented. One case study deals with four heavy vehicles used in a steel mill in Guangzhou, China; and the other deals with 22 buses operated in Changsha, China. The field reliability is measured by monthly average MTBF; the climate conditions are described by monthly average temperature, monthly average relative humidity, and monthly average rainfall. The influence of these variables on the reliability of the vehicles is quantitatively analyzed. It is concluded that the climate conditions have a significant influence on the reliability of the vehicles and the influence can be different in different sites. The analysis is useful for the operational and maintenance management of the vehicles.