Chlorella contains a rich source of biochemical products with applications in the feed, food, nutritional, cosmetic, pharmaceutical and even fuels industries. Chlorella is one of unicellular green algae and is mostly grown in fresh water such as pond and lake. It grows in a manner of nonsexual reproduction so that it multiplies 4~16 times overnight. Large-scale culture is conducted by open pond culture or pure culture using fermenter. Chlorella has various efficacies such as heavy metal removal, degradation of toxic materials, control of arteriosclerosis, immunoprotective effects, anticancer activity and growth-stimulating activity of intestinal bacteria. Chlorella can be used as a taste enhancer and foodstuff, as it has a plenty of essential amino acids, polyunsaturated fatty acids, sterols and chlorella growth factor (CGF). Chlorella is a potential organism which can be utilized for CO$_2$ removal and H$_2$ Production in environmental area and energy Production.