The present study aimed to investigate the biological effects of different concentrations of Ulva lactuca aqueous extract (ULAE) on the growth parameters and biochemical characteristics of Zea mays. The ULAE was applied by foliar spray or directly added to the growth medium of maize plant cultivated in hydroponic system. The growth parameters (shoot length, root length, fresh weight, dry weight and seedling length), minerals, biochemical constituents (chlorophyll content, the activity of ribulose bisphosphate carboxylase (Rubisco), and the detection of Rubisco activase (rca1) gene in seedlings of Zea mays hybrid line (M10) were determined. ULAE was characterized by high abundance of calcium (3255.86 ppm) followed by potassium (287.9 ppm). Among the different treatments, 0.5% and 1% concentration of ULAE as foliar spray exhibited significant effects on growth parameters and biochemical constitutions of the Zea mays seedlings. However, at the higher concentration of ULAE (5%), inhibitory effects were observed. Moreover, as a foliar spray, ULAE at 0.5% and 1% concentration showed a significant effect on seedling length.