Factors affecting annual repair costs were analyzed and a reasonable function was proposed by including more explanatory variables than the previous models for small tractors. Data used in this study were based on a survey of 62 tractors from three selected regencies in Riau Province in 2003. As a result, tractor age, usage, horsepower and operator skill were statistically significant explanatory variables, whereas the ownership system and manufacturer weren’t. Using the proposed model, the annual repair costs were estimated to increase during the expected life of tractors. Changes in usage, horsepower, and operator skill increased more rapidly for annual and cumulative repair costs over the tractor lifespan. Of the significant variables, the effect is more pronounced for operator skill variable. The results suggest that priority should be given to operator training and selection.