This study was designated to determine the costs, returns and relative profitability of BR-29 Boro paddy production in Bangladesh from the viewpoints of small, medium and large farmers of Dewanganj upazila in Jamalpur district. In total 60 sample farmers of which 25 were small, 20 medium and 15 large were purposively selected from each of the selected strata for the study. Primary data were collected from the selected farmers. A simple cost and return analysis was done to determine the profitability of BR-29 Boro paddy production. The major findings of the present study were that BR-29 is a profitable enterprise from the view points of small, medium and large farm groups. The net returns per hectare were Tk.11154, Tk.14854 and Tk. 7046 for small, medium and . large farmers, respectively. Undiscounted BCRs for BR-29 Boro paddy were calculated at 1.33, 1.44 and 1.20 in the case of small, medium and large farmers respectively. Cobb-Douglas production function was also applied to determine the effects of individual inputs on production of BR-29 Boro paddy. It was observed that most of the included variables-had-significant impact on BR-29 Boro paddy under different farm size groups .Out of seven variables included in the function, six variables had positive impact on returns from BR-29 Boro paddy production. The impact of insecticides was negative in the case of medium and large farmers, respectively.