Although Protozoa are well known cause of worldwide diarrhea in immunocompetent and immunocompromised patients, certain genera have emerged as human pathogens in the last decades especially after AIDS epidemic (1-2). In this review it is our aim to call attention of physicians and clinical microbiologists to the following protozoa that can cause diarrhea with increasing tendency.Cryptosporidium parvum causes acute and selflimited diarrhea in immunocompetent patients but chronic and life-threatining diarrhea in immunocompromised patients (1-3). Cyclospora is now well established as a cause of traveler’s diarrhea and endemic disease in developing countries (1). Microsporidia species are being recognized in many cases of previously undiagnosed diarrhea (1).