Macrorhabdosis is a chronic gastric debilitating disease causing loses in most bird’s species. Therefore, this article was designed to outline avian macrorhabdosis disease regarding the incidence, susceptibility, transmission, clinical picture, diagnosis, and control. Macrorhabdosis “formerly megabacteriosis” is a general designation for an important clinically or sub-clinically infectious disease of wild and in-captive companion, psittacin, and passerine birds world wild. Macrorhabdosis is caused by Macrorhabdus ornithogaster (M. ornithogaster) which mainly colonizes the proventriculus close to the proventiculargizzard isthmus. This organism was previously categorized as bacteria, but later it classified as fungus. Infection occurs through ingestion of contaminated feed and water by the droppings or the regurgitation of acute infected or chronic carrier birds. Infected birds M. ornithogaster may appear asymptomatic without signs or show anorexia, depletion, vomiting, diarrhea, and finally death. The lesions mostly constricted to the proventriculus or proventricular/ventricular ismuth as a form of enlargement and thickening with loose koilin layer. Diagnosis of infection is mainly based on microscopic and histopthological examinations and rapid detection of M. ornithogaster using molecular techniques. Application of sanitary and quarantine measures is the must for prevention of infection. Treatment of macrorhabdosis is difficult, however, antifungal and protozoa drugs were satisfactory in certain cases.