Background: Tartrate-resistant acid phosphatase (TRAP) is considered to be a marker of the osteoclast and is also found to be critical for normal development of the skeleton. Objectives: investigating the immunohistochemical distribution of TRAP in some oral tissues of mice at different age points. Methods: Nine male mice from three different age groups (3 mice each) were used in the current study as follows: 1 day aged group, 1 week aged group and adult group. Animals of all groups were sacrificed and sections from skin side of lip, submandibular salivary gland, dorsal surface of tongue and enamel organ were prepared and subjected to histological and immunohistochemical examination to identify the differential expression of TRAP among these tissues. Results: abundant immunohistochemical reaction to TRAP occurred in the granular convoluted tubules of the submandibular glands, in the hair follicles and sebaceous glands of the skin, in the surface layers of the dorsal surface of the tongue and among the different layers of the enamel organ. However, TRAP expression was more intense in the tissues of adult mice than that at earlier ages. Conclusions: TRAP was intensely expressed in the oral tissues of adult mice rather than at earlier ages. These findings indicate that TRAP expression isn't restricted to osteoclasts, and thus, TRAP may be involved in biological processes other than bone remodeling.