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This paper reports development of a thresher for small grain cereal crops. Target small grain cereal crops were sorghum, proso millet, and foxtail millet. A commercially available 2.2-kW soybean thresher was used as a main body, and major design parameters such as rotational speed of the threshing drum (i.e., speed of threshing teeth), opening size of the screen to remove stem part, and air velocity to separate dust and grain. First, design parameters were determined to minimize grain loss to stem and dust discharging exits through factor experiments. For sorghum, selected air velocity, speed of threshing teeth, and opening size of the screen were 4.5 m/s, 13.5 ~ 14.6 m/s, and 10 ~ 12 mm, respectively. For proso millet and foxtail millet, air velocity values were 2.62 and 2.40 m/s, respectively. Teeth velocity was 15.7 m/s and screen opening was 8 ~ 10 mm. Second, a prototype thresher was constructed using the determined design parameters and the performance was evaluated. For sorghum, grain loss weight through stem and dust discharging exits was 5.6% of the total grain weight, and 96.9% of the materials discharged from the grain exit was grain. For proso and foxtail millets, grain loss ratios were 6.47 and 2.18%, respectively. Production cost of the small grain cereal crops would be reduced considerably with utilization of the developed thresher.