Dunaliella algae, which is very rich in .beta.-carotene, can be utilized as an excellent nourishing diet supplement without extracting the .beta.-carotene from the cells of the algae and destroying the .beta.-carotene, in the form of a light impermeable tablet which consists of dried powder of the algae, cyclodextrin, an antioxidant such as vitamin C and vitamin E, a lubricant such as talc and ester of sucrose and fatty acid, a binder such as reducing maltose and starches and a coloring agent such as annato-, caramel-, paprika- or oleoresin-containing sugar solution.