In recent decades, the eutrophication of surface water has become a major environmental concern. Increased concentration of nutrients such as nitrogen and phosphorous lead to eutrophication condition which highlights the demand for effective and economical methods of removing nitrogen and phosphorous from waste water. Bio flocculation using microalgae is an excellent candidate for satisfying the dual purpose of nutrient removal and waste water treatment. It has so many advantages over conventional methods such as toxic free, no chemical is needed, low cost etc. In this review the bio flocculation of microalgae, its mechanisms, applications and harvesting methods are discussed. Keywords: Bio flocculation, microalgae, nutrient removal, waste water treatment