The outer hull or husk of buckwheat (Fagopyrum esculentum Moench.) kernel comprises about 20-30% of the weight of the buckwheat grain. Since it is inedible it should be removed before processing into flour. While imported and expensive dehulling machines are available in Bhutan, to reduce cost and gain wider adoption by farmers and perform the operation efficiently, the Agriculture Machinery Centre (AMC) has developed a buckwheat dehuller based on the impact and shear principle for efficient dehulling of whole buckwheat with most of the machine's body parts available locally. The present study was carried out to test the machine and to evaluate the best operating impeller speed for efficient dehulling of buckwheat. The machine was tested at five different levels of impeller speed: 1,700, 1,800, 1,900, 2,000 and 2,100 revolutions per minute (rpm). Process performance of dehulling efficiency (DE), and broken percentage (B%) were measured at each rpm. There was a significant difference in DE and (B%) across the five different speeds. The best DE of 88.94 % was observed at 2,100 rpm. However, there was also a high correlation between dehulling efficiency and the proportion of broken kernels, with the highest broken percentage of 43.96% observed at 2,100 rpm.