Agricultural research is a big business and plays an important role in country development. This work aims to estimate the economic benefit provided to the Thai economy by investments in cassava research in the past. To complete this study, secondary data regarding cassava planting area, crop production, prices and investment funds expended for cassava research were gathered from the Office of Agricultural Economics, the National Research Council of Thailand, the Thai Tapioca Development Institute, Department of Agriculture, and Kasetsart University, during the years 1976 to 2014. Based on the data, cassava area and yield response functions were evaluated. The results shows that investment in cassava research at the present, as in the past, are determined significantly by the expansion of cassava area and yield; that is, investment in cassava research helps to increase cassava yield significantly. The marginal value product of research found in the study indicates that for each dollar invested in cassava research has resulted in economic benefit of 1.63 times the cost in the short run and 2.21 times the costs in the long run. Hence, investment in cassava research is worthwhile to the Thai economy, and continuing cassava research projects is highly recommended to produce technological innovation in support to agricultural development and transformation in Thailand.