Vital pulpotomy is a very useful method for disarming of canine tooth, tooth fracture, periodontitis, and malocclusion in veterinary dentistry. Calcium hydroxide is the material commonly used as a liner during vital pulpotomy. This creates a mineralized barrier by stimulating osteoblastic hard tissue repair, arrests the inflammatory response, and soothes dentin. However, the powder or mix type calcium hydroxide materials have many disadvantages due to complicated procedures for use and are hard to handle when vital pulpotomy is followed under general anesthesia in animals. This study was conducted in order to compare the effect of mix and premixed paste type calcium hydroxide as a liner in vital pulpotomy. Six beagle dogs underwent hemisection on the mesial root of the mandibular first molar and vital pulpotomy on the distal root of the first molar. On the distal root of the left and right mandibular first molar, mix type (DYCAL®, Dentsply, USA) and premixed paste type calcium hydroxide (VITAPEX®, Morita, Japan) were used as liners, respectively. Radiological evaluation was performed at immediate, 4, 12, and 20 weeks after vital pulpotomy. According to the results, all teeth had well-formed dentinal bridges, and there were no periradicular lucency, lamina dura loss, or anomalies of the pulp cavity. According to these results, on vital pulpotomy in animals, premixed paste type calcium hydroxide was easy to handle and decreased the anesthesia period due to a more convenient application procedure. A further study of many clinical cases is needed for evaluation of side effects and other problems.