Seeds of Lactuca sativa were germinated in culture medium containing microalga (Chlorella vulgaris) and grown for 3, 6, 9, 12 and 15 days in order to study its effect on growth parameters and some physiological response of seed germination and growth. In general, microalgal treatment significantly increased the growth with a significant decrease in soluble carbohydrate, soluble protein and total free amino acids compared with those of the control (sterilized culture medium) of seed germination. Addition of microalga to the culture medium or soil significantly increased fresh and dry weight of seedlings as well as pigments content. The best treatments were 2 and 3 g dry alga kg^-1 soil.