BACKGROUND: In dogs, an insufficient variety of cell lines commercially available or difficulties in obtaining the existing cell lines developed from various studies results in a limited number of cytotoxicity and related molecular studies integrated with clinical practice. Hence, the doses of many drugs or supportive treatments used in canine tumor cases are adjusted based on studies in humans. OBJECTIVE: A cell line was established from a benign mixed tumor of the canine mammary gland. METHODS: Following surgical removal of the tumor, mechanical dissociation, and PBS washing, a culture process of the tumor cells was performed, including the passaging, freezing, and thawing stages. After several passages, the morphological characteristics of the cells at the logarithmic growth phase were observed under a phase-contrast microscope. RESULTS: The microscopy of the cells cultured on plastic dishes revealed monolayer colonies. The average passage time, which was 5-6 days in the first three passages, decreased to 2-3 days after the third passage. Microscopic examination of tumor cells revealed an adherent, stellated, and spindle-shaped structure. CONCLUSIONS: No difference was observed in the viability and morphology of the cells thawed even after the long period of freezing (∼18 months). The different canine cell lines can provide promising molecular applications that can be adapted into practical clinics in veterinary science.