This paper estimates the economic impacts of oilseed research and development (R&D) in Bangladesh. For the purpose, a total of 1,980 oilseed growing farmers are randomly selected from 11 oilseed growing districts in the country for gathering primary data using pre-tested interview schedules during 2011-12. An ex-post evaluation method using economic surplus model under both closed and small-open market economy situations has been adopted to estimate the rate of returns of investment in oilseeds R&D. The adoption of improved mustard, groundnut, sesame and soybean varieties at the farm level creates an additional employment of 12.7, 11.6, 15.4, and 6.1 man-days/ha for the respondent farmers respectively. The livelihood status of the adopting households is much better than that of non-adopting households. Ex-post evaluation of the past investment on oilseeds R&D reveals an IRR of 24 per cent, which ranges from 22 per cent to 26 per cent under different assumptions. The amounts of NPV and foreign exchange savings due to R&D of oilseeds during 1998-2012 are Tk. 4,769.04 million and US$ 97.11 million respectively.