Two pot experiments were conducted during two successive sea-sons 1995/1996 and 1996/1997 to investigate the effect of different levels of soil available water (100%, 75% 50% and 25%) on four sugar beet varieties (Beta vulgaris L.) The results indicated that: - Growth and yield of sugar beet shoot were affected by water deficit more than the corresponding roots. • In spite of increasing sucrose percentage in root juice, purity and sugar yield per plant were decreased under water strees. - Biosynthesis of chlorophyll A was more degraded by water stress than chlorophyll B or carotenoids. - Nitrogen and sodium concentrations in both root and leaves were more reduced than phosphorus and potassium with lowering soil moisture availability at 50% and 25% from control. - Proline concentration increased in sugar beet leaves while acid inver-tase activity was inhibited in plant's roots under drought condition. - Varieties of sugar beet significantly differed in their response to water stress; both Ras Poly and Del 939 varieties were less affected by water deficit. M 9340 variety was the most sensitive. Top variety was moder-ately affected. - The increase in free proline concentration under water stress was much higher in the leaves of tolerant sugar beet varieties than that in the sensitive ones. This proved that proline plays a role in drought toler-ance in sugar beet. - Varieties of sugar beet could be arranged ascendingly according to their root invertase activity. Ras poly, Del 939, Top and M 9340.