The current study is designed to investigate the histological and immunohistochemical characteristics of the thyroid gland in adult male Sciurus anamalus. This study found that the thyroid gland of the Caucasian squirrel is located in the neck area, below the larynx, on both sides of the trachea. It has two lobes (right and left) with cylindrical shape. The histological studies revealed that the thyroid gland is surrounded by a capsule which consists of connective tissue and forming of two layers which are outer layer and inner layer, and a layer of adipose tissue appears overlapping the outer layer. The inner tissue of the gland consists of follicles with different shapes and sizes, and is lined with simple cuboidal epithelial tissue (follicular cells). Sometimes it appears in the form of high or low cuboidal epithelial tissue, in dependent on the functional activity state of the gland, and the follicles cavities are filled with colloid. In addition, there are two kinds of cells spread in the gland tissue, follicular cells and parafollicular cells, and they are fewer in number and larger in size than follicular cells and appear either singly or in the form of clusters and occupy two sites between the follicles or within the follicle. Immunologically, the results observed an immune response to thyroglobulin antibodies to detect the protein secreted by the follicular cells, which in turn secreted it to the colloid. Moreover, the immune response appeared clear in the cell membrane of the follicular cells and the colloid through the appearance of the brown color which is specific to the immune reaction. Keywords: