BECAUSE of the economic importance of sugar beet (Beta vulgaris L) in sucrose production, a field experiment was conducted to elucidate the key regulators of sucrose metabolism in source leaves and sink roots at 135, 150, 165 and 180 day after sowing (DAS) that would be determined sucrose yield. Increase in sucrose phosphate synthase (SPS) activity in source and sink tissues during the first three selected harvest phases was associated in leaves with an increase in activities of acid invertase (AI) and neutral invertase (NI), chlorophyll a, total chlorophyll and reducing sugars on the one hand and the levels of sucrose and inorganic phosphorus (Pi) in roots on the other hand. The maximum sucrose level in roots was at 165 DAS. A gradual increase in root NI activity accompanied by an increase in reducing sugars and a decrease in the sucrose/reducing sugars ratio in roots by harvest date progress was observed. Pearson correlation test revealed contradictory findings whereas, SPS activity correlated with sucrose level in leaves negatively but positively in roots. All investigated enzymes in leaves correlated negatively with sucrose/reducing ratio. But in roots, only NI activity correlated negatively with sucrose/reducing sugars ratio.