Juice purification is one of the most important steps in sugar beet industries and the main aim in separation of non-sucrose substances in raw juice and reach to thermo-stable and highly pure juice for the subsequent processes such as concentration and crystallization. In conventional methods, preliming is the first step of juice purification and has an important role in purification process. In this study, the evaluation of optimum condition in preliming step in sugar beet industries in constant temperature (55°C) was conducted. In order to determine the effects of alkalinity (0.16, 0.18, 0.20, 0.22, and 0.24 gCaO/100ml juice) and time duration (20, 25, 30, and 35 min.) on the raw juice, a completely randomized experiment with factorial arrangement and three replications was conducted. Parameters were evaluated include sedimentation rate, color, pH and purification index. The results showed that there is significant difference between alkalinity levels in respect of the effect on sedimentation rate, color and purification index (P<0.01). In addition, a significant difference was seen between time and sedimentation rate, color and purification index (P<0.01). According to these results, the alkalinity value of 0.22 gCaO/100ml juice and pH value of 11.6 with medium value and 30 min. is the best condition for increasing sedimentation rate and purification index and reducing the color

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