This study has been carried out to extract the stevia sweetener, sugar substitute, from the leaf ofrnstevia plant. Solvent extraction of the leaf using hot water was investigated. The main andrninteraction effects of temperature, extraction time and material ratio (stevia leaf: water) werernexamined. In the main effects investigation all the main factors had a significant effects on thernyield of stevia sweetener. But in the interaction effects, only temperature with material ratio andrnextraction time with material ratio had a significant effect on the yield of the sweetener. Therninteraction effects of temperature with extraction time (residence time) had no any significantrneffects on the yield of stevia sweetener. The two factor interaction model was developed. In thisrnmodel the term which had no significant effects had been reduced. This term was the interactionrneffect of temperature with residence time (Ï„Î²)ij. Different analysis of the data such as analysis ofrnthe variance, hypothesis testing and predicted R-squared also enforce this idea. The p-value wasrn0.1270 which was greater than type one error 0.05. The F-calculate for this term was 1.74 thatrnwas less than F-tabulate 1.90. The predicted R-squared was 60.10% that was far from thernadjusted R-squared 87.49%. These different analysis leads to the reduction of the interactionrneffect of temperature with residence time from the model. The model adequacy also investigatedrnby normal probability plot of residuals and plot of residual verses predicted value. Both normalrnprobability plot as well as residual verses predicted value plots showed that the model wasrnacceptable. Optimum conditions for the extraction process were optimized. The optimalrntreatments of each factor to maximize the yield were, for the temperature 50oC, three hours forrnthe extraction time and 1:10 material ratio. The maximum yield that was obtained at thesernoptimum conditions was 49.90 %. The two methods report form and ramp form of optimizationrnshowed the same result or the same conditions.