Two field experiments were performed at the Horticultural Research Farm of El-Bramoon (Dakahliya Governorate) during 1998 and 1999 seasons. This study aimed to study the effect of mineral nitrogen fertilizer levels, sources , biological fertilization and their interaction on chemical composition of sweet potato tuber roots. The main results could be summarized as follows: Application of Ca (NO₃)₂ fertilizer significantly increased reducing sugars contents, K, NO₂- and NO₃- contents in tuber roots as compared with (NH₄)₂ SO₄ fertilizer. In addition, (NH4)₂ SO₄ fertilizer had significant increases on total carotene content in tuber roots. Inoculation of plants with biofertilizer (nitrobien) led to increase reducing sugars and total carotene contents in tuber roots and beside that significantly reduced NO₃-, and NO₂- concentrations in tuber roots comparing with the uninoculated ones. Raising nitrogen fertilizer levels from 0 to 80 kg N/fed resulted in a significant increase in total soluble and reducing sugars, total carotene as well as  N, P, K, NO₃- and NO₂- concentrations in both seasons. The positive interaction between N-sources and biofertilizer have been observed, application of Ca (NO₃)₂ fertilizer with biofertilizer gave the highest values of total soluble sugars NO₃- and NO₂- concentrations in tuber roots comparing with (NH₄)₂ SO₄ with biofertilizer. Application of  (NH₄)₂ SO₄ fertilizer with biofertilizer significantly increased total carotene content. The interaction between nitrogen fertilizer rates and biofertilizer had significant effect on reducing sugars, K, NO₃- and NO₂- concentration. Thus, it can be recommended that adding (NH₄)₂ SO₄ at 60 kg N/fed with biofertilizer (nitrobien) was the best treatment under the condition of this study for reducing mineral nitrogen fertilization, soil pollution and improving quality of tuber roots.