Blastocystis is anaerobic, unicellular protozoan resides in intestinal tract of human as well as other hosts. Despite the various observations over the year, the classification of Blastocystis Species still controversial and it is difficult to define its taxonomical status. There are variations in morphological forms of Blastocystis hominis but three major forms commonly noted: vacuolar, granular, ameboid. The pathogenicity of Blastocystis is still matter of debate. A number of studies have shown the pathogenic potential of this organism. Hence, in this review, we will discuss classification, morphology, lifecycle, pathogenicity, Clinical features, Diagnosis and treatment of Blastocystis.