Abstract: The performance of the machine was evaluated in terms of separation and cleaning efficiencies, and separation and cleaning losses at different feed rate, sieves oscillations and sieves inclinations; three levels of sieve slopes (0, 5 and 10 degrees), four levels of sieve oscillation (5, 10, 15 and 20 Hz) and four levels of feed rates (3, 6, 9 and 12 kg/min) were used. The experimental design was factorial in split-split plot. The prototype tef grain separating and cleaning machine had the ability to winnow the premature grains, chaff and leaves, which are lighter than grains. It was also capable of reducing time wastage, grains loss, labour requirement and contamination. The performance evaluated in terms of separating efficiency, cleaning efficiency, separation loss and cleaning loss at different sieve slopes, sieve oscillations and feed rates indicate that the separation and cleaning losses increased with increasing sieve oscillation and feed rate for all sieve slopes. But the separation and cleaning efficiencies decreased with increasing sieve oscillations and feed rates at all sieve slopes. The minimum losses and the maximum efficiency were achieved at 5o sieve slope for all sieve oscillations and feed rates. The separation efficiency, cleaning efficiency, separation loss and cleaning loss were 97.94, 98.58, 0.71 and 0.7%, respectively at sieve oscillation of 5 Hz, feed rate of 3 kg/min and sieve slope of 5 degrees. The separation efficiency, cleaning efficiency, separation loss and cleaning loss were 52.71, 39.88, 25.62 and 34.5%, respectively, at sieve oscillation of 20 Hz, at feed rate 12 kg/min and at sieve slope of 5 degree.