This study show the effect of applied vitamins ascorbic acid (vitamin C) and thiamine (vitamin B 1 ) on growth criteria, total photosynthetic pigments, total carbohydrate contents, total protein contents, free amino acids and proline of Chlorella vulgaris Beijer cultured for 7 days. The growth criteria (cell number and dry weight), total photosynthetic pigments, total carbohydrate contents, total protein contents, other free amino acids and proline of Chlorella vulgaris Beijer cultures were significantly increased when the algal cultures were subject to lower levels (1.5 and 3 ppm) of MgCl 2 only. On the other side, under moderate and higher levels ( 45 and 6 ppm) of MgCl 2 the cell number , dry weight, total photosynthetic pigments, total carbohydrate contents, total protein contents and other free amino acids of stressed Chlorella vulgaris Beijer cultures were significantly decreased. However, the soluble carbohydrate contents, soluble proteins and proline of Chlorella vulgaris Beijer cultures were significantly increased. Also, the growth criteria (cell count and dry weight), total photosynthetic pigments, total protein contents, other free amino acids and proline of Chlorella vulgaris Beijer cultures were significantly increased, when the algal cultures were subject to various levels (1.5, 3 4.5 and 6 ppm) of MgCl 2 and treated with 200 ppm of either ascorbic acid or thiamine. However, the different carbohydrate fractions (soluble, insoluble and total carbohydrate), soluble proteins of Chlorella vulgaris Beijer cultures were significantly decreased. All these parameters content were compared with that those of the control cultures.