Two field experiments were conducted in a sandy soil at Um Saber village, Kom Hamada, (latitude of 30.52^° N and longitude of 30.79^° E), El-Beheira Governorate, Egypt, during 2017/2018 and 2018/2019 seasons to find out the optimal levels of phosphorus, boron and magnesium to get the highest yield and quality of sugar beet. Sugar beet variety "Hamza" was sown. RCBD in a split-plot arrangement was used to lay out 27 treatments, represented the combinations of three phosphorus (P) levels (15, 30 and 45 kg P₂O₅/fed), three foliar levels of boron "B" (zero, 75 and 150 ppm) and three magnesium "Mg" levels (zero, 5 and 10 g MgSO₄.7H₂O/l). Raising P-level to 30 kg P₂O₅/fed considerably increased sucrose%, extracted sugar% (ES%), quality index (QI), sugar yield/fed in the 2^nd season, as well as root diameter, root fresh weight/plant (RFW) and root yield/fed, while, sugar lost to molasses (SLM%) was markedly decreased. Increasing B-level to 150ppm appreciably increased RFW, sucrose%, ES%, QI, root and sugar yields/fed. Raising Mg-fertilizer level to 10 g/l sharply increased RFW, sucrose%, ES%, QI, root and sugar yields/fed in both seasons, while SLM% substantially reduced in the 2^nd one. Effects of the significant interactions among phosphorus, boron and magnesium levels on the studied traits were discussed. Under the environmental conditions of this study, adding 30 kg P₂O₅/fed to the soil + spraying 150 ppm boron + spraying 10 g MgSO₄.7H₂O/l could be recommended to attain economical root and sugar yields/fed, as well as the best quality of sugar beet.