This study investigated the quality of tofu prepared by treating soybean milk with deep seawater as a coagulant. The quality and shelf-life of the tofu prepared using the deep seawater coagulant were determined and compared to those using $CaSO_4$, surface seawater, and intermediate seawater coagulant. The tofu made with the deep seawater coagulant was firmest. In addition, the deep seawater tofu product had more, smaller particles in the microscopic view, compared to the tofu made from surface and intermediate seawater coagulants. The deep seawater tofu product had the lowest viable cell counts and turbidity. In addition, the deep seawater tofu product had a longer extended shelf-life. From these results, deep seawater appears to improve the texture, taste, and shelf-life of tofu when used as a coagulant.