This study was carried out to identify the histological structures of the ovary and the related uterine tubes of the adult guinea pig (Cavica porcellus). To conduct such project, 14 adult guinea pigs at their diestrous period were collected from the local breeders directly. Animals were euthanized, dissected and subsequently ovaries and specimens from uterine tubes were collected and fixed by 10% neutral buffered formalin and some of specimens were fixed in Bouin's solution for subsequent histochemical staining then subjected to routine processes such as dehydration, clearing, embedding and block preparation. Sections of 6 µm were prepared and stained with hematoxylin-eosin, Masson's Trichrome, Alcian blue (pH 2.5) and Periodic acid shift stains.
       Gross findings showed two bilateral rounded and slightly elongated ovaries situated in the abdominal cavity suspended by mesovarium ligament. Microscopic findings revealed prominent large follicles and to a lesser extent, the small and medium types in the ovaries of adults studied guinea pigs. The data showed the presence of many pre-ovulatory follicles during the diestrous period in this polyestrous species. Gross findings of the uterine tubes revealed the presence of bilateral uterine tubes. Each tube included short straighten preampulla which was expanded cranially to form infundibulum, coiled long ampulla and finally the isthmus, the shortest and straight part traversed the cranial end of the uterine horn. Microscopically, all of the uterine tube was lined with simple columnar epithelium. Mucosa showed very long and branched mucosal folds in the pre-ampulla, for lesser extent in ampulla but shortest and widest in isthmus. Tunica muscularis was absent at infundibulum, thinnest at pre-ampulla, whereas, the thickest in isthmus. Histochemically, the non ciliated columnar cells (present mainly in the isthmus and few in ampulla) were stained positively with AB and PAS stains.