Abstract: Background and Objective: Traditional paddy threshing is still usually carried out by women and children in the rural village. The aim of this study was to design and develop a tangential thresher, optimize the conditions necessary for threshing paddy using a response surface modeling methodology. Materials and Methods: Paddy straw (Faro 44 variety) was used for this study. Moisture contents at three levels between 14.50 and 25.10% and threshing drum speed between 398 and 565 rpm. The response surface of desirability function was used for the numerical optimization. Results: Some of the performance efficiencies (cleaning efficiency, threshing recovery, threshing efficiency, percentage loss and percentage blown grain) which was evaluated were significantly (p<0.05) affected by moisture content and threshing drum speed. Conclusion: The effects of the moisture content, threshing drum speed and its optimization were regarded as very useful to ascertain the performance efficiency of the developed tangential flow threshing machine.