The aim of this research is to examine the performance of clarification unit at Wonji-Shoa sugar factory and setting optimum values for main clarifying reagents to improve the efficiency of clarification plant. The performance of the clarification plant has been evaluated in terms of main clear juice quality parameters (turbidity, purity rise, mud volume and CaO content). In addition, the effect of raw materials quality (cane, lime and sulphur) on clarification performance also studied. Currently most clarification measuring parameters except CaO content were performing below the desired. The average result of the assessment shows that 0.13%, 1953 IU, 40% and 765ppm of purity rise, turbidity and mud volume respectively were as the standard was expecting 1 - 1.5 %, 700 - 1500 IU, 25 % and < 800 ppm purity rise, turbidity, mud volume and hardness of clear juice respectively. This indicates that there were sucrose loss and insufficient removal of nonsugar materials during the clarification process. Processing low quality of cane and lime in terms of the addition of high amount of extraneous matter > 10 % and MgO content above 12 %, improper controlled parameters mainly milk of lime density and temperature were the main problems examined in this study. Those problems were the main causes for the poor performance of clarification by increasing turbidity, mud volume and disturbing the settling of the flocs at Wonji-Shoa sugar factory. Optimization on the dose of main clarification reagents were done for efficiency improvement of clarification plant by varying the effect of pre- liming pH (for the level of 7.7, 8, 8.5, 9, 9.3); sulphited juice pH (for the level of 6.6, 6.8, 7, 7.2, 7.3) and flocculant level (1.3, 2, 3, 4, 4.7 ppm). The main response variables were purity rise, turbidity, settling rate, mud volume and calcium contents of clear juice. The data obtained from the comparative experiments were analyzed through design expert software using central composite design. The optimal results of purity rise, turbidity, CaO content, settling rate and mud volume were 1.57, 738 IU, 758 ppm, 0.055 cm/s and 229 ml (22.9 %) respectively with the respective pre- liming pH ,sulphited juice pH and flocculant dose 8.29, 7.13 and 4 ppm. So practicing the above optimum conditions can increase productivity and quality of sugar and minimize the sucrose loss in Wonji-Shoa Sugar Factory.