Abstract: A field experiment was carried out at the Research Center of Barkat-e-Jovein, Jovein agro-industries, Northeastern Iran, during 2008 to evaluate the effect of concentration and time of boron foliar application on root yield and quality of sugar beet (Beta vulgaris). Treatments consisted of 3 application times (30, 45 and 60 DAP) and 4 application rates (spraying with concentrations of 0, 4, 8 and 12% corresponding with 0, 0.35, 0.70 and 1.22 kg B ha-1 as water-soluble B (Boric acid)). Results revealed that application time had neither any considerable effect on sucrose concentration, root yield, k+, Na+, molasses sugar, nor on reducing nitrogen. Boron application increased root yield and sucrose concentration by 12.12 and 26.35%, respectively decreasing k+, Na+, α-amino-N and molasses sugar compared with those of the control. In this study, no significant differences were found to exist between boron application times. On the other hand, the highest root yield and sucrose concentration were obtained by spraying with 12% boric acid at 60 days after planting.