Ultraviolet (UV) rays cause skin damage. Chronic exposure to UV irradiation causes decreased collagen synthesis, degenerative changes in collagen bundles, accumulation of elastotic material and increased epidermal thickness. Origanum hypericifolium, an endemic Turkish plant, belongs to Lamiaceae family. The main constituents of its oil are monoterpenes including cymene, carvacrol, thymol and γ-terpinene. The effects of undiluted O. hypericifolium oil on UVB irradiated skin of mice were investigated histochemically. Four groups of female BALB/c mice, whose dorsal hair was shaved, were allocated as follows: non-UVB irradiated (Group 1), UVB-irradiated (Group 2), O. hypericifolium oil treated (Group 3), and O. hypericifolium oil treated and UVB irradiated (Group 4). Sections of dorsal skin samples were stained with Mallory's phosphotungstic acid hematoxylin for collagen fibers and Taenzer-Unna orcein for elastic fibers. Sections also were stained with hematoxylin and eosin to measure epidermal thickness. We observed intense staining of collagen and homogeneous, scattered thin elastic fibers in Group 1; scattered and weakly stained collagen and curled, amorphous, accumulate elastic fibers in Group 2; and intense staining of collagen in Groups 3 and 4. Accumulation of elastic fibers in the dermis was unremarkable in Groups 3 and 4. In Groups 3 and 4, O. hypericifolium oil treatment thickened the epidermis. Epidermal thickness was greatest in Group 4. We suggest that O. hypericifolium oil may block UVB induced alterations of collagen and elastic fibers, and increase epidermal thickness.