Algerian coast contains a high species diversity of marine algae; however, there are only few reports on their bio-stimulant properties. Different concentrations of the brown seaweed Cystoseira mediterranea . Extracts were used to determine their efficiency as biostimulant of barley growth and productivity. All growth parameters and chlorophyll content were found to be highest at the 50% concentration. Our results have clearly shown that algerian seaweed extract could serve as an alternative to chemical fertilizers, as is abundant, with high quality, ecofriendly, and deliver environmental and economic benefits to farmers.