The effect of alginate concentration on the mechanical properties of hydroxyapatite (HAp) scaffold was investigated in this study. Sodium alginate solution with concentration 1%, 3% and 5% was prepared through the neutral extraction of cultivated Sargassumpolycystum brown seaweed. HAp scaffold was prepared via polymer reticulate method and sintered at 1250 ̊C. HAp scaffolds were then immersed in sodium alginate solution at 1%, 3% and 5% concentration under vacuum. FTIR spectra show that the extracted sodium alginate has the same functional groups as in commercial sodium alginate. Compressive strength increased as the sodium alginate concentration increased. Morphology observation shows that the micro cracks on the struts were covered by alginate. The increase in the compressive strength is due to the coverage of the cracks on the struts by sodium alginate.