The objective of this study was to obtain the best sodium alginate extract from Padina sp. with different potassium hydroxide concentration and the study quality of contained sodium alginate. Padina sp. was collected on December 2016 in coastal Senggarang, Tanjungpinang, Riau Islands Province. The method in this study the raw material of Padina sp. was extraction by potassium hydroxide with concentration (0.6%, 0.8%, 1%). We analyzed content of moisture, ash, yield, viscosity and pH. The best results obtained in the treatment with a solution of KOH concentration 0,8% with moisture content 10,87%, ash content 31,24%, yield 17,82%, viscosity 275,50 cP and pH 8,21.