TWO FIELD experiments were conducted at Wadi El-Natrun, El-Bahira Governorate, (latitude of 30.480 N and longitude of 30.500 E) during 2013/2014 and 2014/2015 seasons to study the impact of foliar application with alga extract (Spirulina platensis) and boron on yield and quality of sugar beet (Beta vulgaris var. saccharifera, L.) planted in a sandy soil under sprinkler irrigation system. The present work included sixteen treatments, represented the combinations of four alga extract levels (without; 1.5; 2.5 and 3.5 g / liter) sprayed twice at 4-6 and 6-8 leaf stages as well as four concentrations of boron (without; 50; 100 and 150 ppm/liter/fad, as boric acid 17% boron) which, sprayed twice at 6-8 and 10 leaf stages. The treatments were arranged in a strip plot design in three replicates. The vertical plots were occupied with four levels of alga extract and the horizontal plots were devoted to the four levels of boron. The Results indicated that foliar application of alga extract using 2.5 g/l or 3.5 g/l produced significantly higher values of photosynthetic pigments (chlorophyll a, b and carotenoides), vegetative growth traits of sugar beet plants (root diameter, root and foliage fresh weight), (root and top dry weight/plant), extractable sugar %, quality index ,nitrogen, phosphorus, potassium, boron contents in leaves and root, top and sugar yields/fad, as well as the lowest content of sodium in roots in both seasons. Higher values of root diameter, fresh weight/plant, root, top and sugar yields/fad, sucrose, extractable sugar, quality index percentages and boron contents in leaves and roots, at harvesting time, were obtained with spraying boron at 100 ppm/fad in both seasons. The interaction between alga extract and boron levels significantly affected chlorophyll (a), root fresh weight/plant in both seasons; chlorophyll (b), and root yield/fad in 1st one. The combination of 3.5 g/l alga extract along with 100 ppm boron can be recommended to get the maximum root yield/fad (27.13 t/fad) in 1st season, which showed an integrative role between fertilization using the alga extract and boron.