The abiotic stress can significantly affect plant growth and its biochemical traits, consequently the economic yield of crops. Therefore, our study aimed to investigate the effects of seaweed extract application (i.e. 0, 100 and 300 ppm red algae extracts) on growth, biochemical and tolerance traits of salt-sensitive Phaseolus vulgaris seedling grown under saline stress conditions (50 and 100 mM NaCl). Plant growth traits and chlorophyll contents were significantly decreased when plants were grown with saline treatments. However, seaweed treatments either 100 ppm or 300 ppm mitigated the salt stress and significantly improved the total phenolic, proline, pigments contents and enzymes activity. Saline stress resulted in an increase in the electrolyte leakage (EL), while the seaweed extraction treatments minimized EL and malondialdehyde (MDA) contents. In addition, proline content and antioxidant enzymes activity were significantly increased in the response to salt stress treatments. Compared to the 300 ppm of the algae extract, it was clear that the red algae extract at 100 ppm was the optimal treatment in terms of improving plant growth and biochemical traits when plants grown under the highest level of saline stress (100 mM NaCl). In conclusion, treating seeds of crops with the algae extracts can significantly mitigate the harmful effects of saline stress.