Evaluation of yield potential can provide valuable information for a strategic plan to increase yield of soybean in Thailand. However, this process is time consuming and expensive. A dynamic soybean model provides an alternative option to simulate yield under various growing conditions. The objective of this study was to evaluate the performance of the CSM-CROPGRO-Soybean model and to determine soybean yield potential and yield reduction due to rainfall limitation for growing conditions in northeastern Thailand. Data from two experiments that were conducted in 1991 at Chiang Mai University and in 2003 at Khon Kaen University were used to determine the cultivar coefficients for the cultivars CM 60 and SJ 5. The model was evaluated with data from two experiments that were conducted at Chiang Mai University and was then used to determine yield gaps attributed to rainfall limitation for these two varieties and four different planting dates. The results indicated a good agreement between simulated and observed data for phenology and growth of soybean and demonstrated the potential of the model. The analysis with long-term historical weather data showed that the cultivar CM 60 is more suitable for growing conditions in the district of Phu Pha Man than SJ 5. Yield reductions due to limited rainfall ranged from 11 to 26 %, and were generally greater for the late planting dates than the early planting dates. A larger amount of rainfall during the early season planting dates contributed to a smaller percentage in yield reduction, indicating that these planting dates are more appropriated for soybean production when compared to the late season planting dates. This study showed that the CSM-CROPGRO-Soybean model can be a helpful tool for quantifying the yield potential and yield gaps and could be applied to other production areas in Thailand.