Based on all previous researches on using natural biomaterials to develop physical and mechanical properties of mortar, the extracted gel from the flaxseed as bio-admixture is examined and tested as a sustainable chemical admixture in the production of cement mortar, as well as determining its influence on some mechanical and physical properties such as compression strength, flexural strength, workability and water absorption) of mortar. Flaxseed gel was added to mortar mixes with the percentage of 5%, 10% and 15% as a partial replacement by weight of mixing water. FTIR spectroscopy for flaxseed has been performed to identify organic/inorganic components. The effect of flaxseed gel in the mortar structure was evaluated, and the results showed a good enhancement in the properties of mortar caused by using variable percentages of gel replacement in the mixture in which, the compressive strength of cement mortar exhibited a significant increase to 56.3% by replacing 15% of mortar cement with flaxseed gel, while the higher increase in flexural strength reached 25.6% was achieved by replacing 5% of mortar cement with gel. There is a slight increase in the water absorption of mortar mixture containing 15% of flaxseed gel which reached 5.7% compared to 4.3 % achieved by the reference mixture.