This study attempts to analyse the energy flow in boro rice production in the south-west coastal region of Bangladesh during the dry season (November 2010 to May 2011). Structured questionnaire survey was made of target farmers of five farm sizes in randomly selected five coastal villages to collect step-wise and source-wise quantitative energy inputs and outputs. The energy from seed bed, land operation and maintenance, and harvesting and threshing were calculated as step-wise energy input, whereas energy from human labour, machinery, seed, irrigation, and fertilizer and pesticide applications were calculated as source-wise energy input. The output energy was estimated based on the main product (rice grains) and by-product (straw) of rice cultivation. Energy input, energy output and energy efficiency of rice cultivation were calculated in average of five coastal villages for each of the farm sizes. The results reveal that the average total energy input was estimated to be 44,520 MJ ha-1, which varied from 29,283 MJ ha-1 on medium farmers to 72,339 MJ ha-1 on landless farmers. The total energy use in all steps decreases with an increase in size of farm holdings, except large farm. Seedbed stage consumes the highest energy following land operation and maintenance, and harvesting and threshing. Fertilizers accounted for a major share (63.3%) of energy input followed by seed, irrigation, machinery power, pesticides and manpower. In average farm situation, the total energy output produced from the field was 80,690 MJ ha-1n , which varied from 51,641 MJ ha-1 on large farm to 142,593 MJ ha-1 on landless farm. In the same situation, main product (rice grain) and by-product contribute respective 79.2% and 20.8% in the total output energy. Total energy output also decreased with the increase in farm size. The energy efficiency (output/input) from rice cultivation ranged from 1.5 on large farm to 2.0 on landless farm with an average of 1.8. The output-input ratio of energy was estimated to be in the sequence of landless > marginal > medium > small > large farm. Therefore, lower sized farms are more energy efficient than those of larger sized farms in rice production in the south-west coastal region of Bangladesh.