Abstract: This study was conducted to investigate the combine harvester speed, threshing cylinder speed and concave clearance on threshing losses and some related parameters during harvesting the local rice variety forate 39. The experiment was designed as a split-split-plot design on the basis of RCBD with three replicates. A class dominator 68 sec combine harvester was used to conduct all the trails. The results revealed that all factors of the study had a significant effect on threshing losses at p≤0.01. A smallest concave clearance, highest threshing cylinder speed and lowest combine advancement resulted in a lower threshing losses. While the highest value of losses achieved at a large concave clearance, lowest threshing cylinder speed and highest combine advancement. The results also suggested a strong correlation relationship between the study parameters. Regarding the threshing loss parameter, it was significantly and positively correlated with the feed rate while negatively correlated with threshing index at p≤0.01.