Background: Plastics in the environment have provoked increasing worries in recent years, and recurrently, plastic waste is increasingly being discharged into water resources including rivers, where it breaks down into smaller particles. Objective: Investigate the histological and histochemical effects of two types of microplastics (MPs) in the gills, liver, and kidney of Nile tilapia (Oreochromis niloticus). Methods: The study included seven groups of O. niloticus fingerlings, the first was set as a control and the remainders were fed on a diet containing three different concentrations of two types of microplastics; namely low-density polyethylene (LD-PE) and polyethylene terephthalate (PET). Results: Chronic administration of MPs induced different histopathological lesions in fish gills, liver, and kidney. The prevailing histological changes in fish gills were hypertrophy, hyperplasia, lamellar aneurysm, and fusion of lamellae, while the liver showed hypertrophied hepatocytes, vacuolation, blood vessels congestion, karyolysis and pyknotic nuclear hepatocytes, necrotic cells, and hydropic degeneration. Meanwhile, the renal tissue of MPs-fed fishes delineated lymphocytic infiltration, degenerated renal tubules, obliteration in Bowman's space, and necrotic areas. These lesions were more obvious with high concentrations of MPs, LD-PE, or PET. Histochemically, feeding of diets containing MPs induced significant depletion in each of glycogen and total protein contents of the liver, and kidney of experimental fishes as compared with control.