The increase in the lifespan of small animals has enlarged the number of diseases such as mammary neoplasms, which represent 50% of all tumors. The treatment of these neoplasms is to perform mastectomy. The pain results mostly from inflammation; cardinal signs are redness, swelling, pain and heat. The thermographic camera converts heat into images on the camera's display. This study aimed to evaluate and correlate the inflammation and pain score on bitches undergoing mastectomy. This descriptive study was conducted in five spayed bitches undergoing unilateral mastectomy. Thermographic evaluation and application of pain scales (short form of the Glasgow Composite Pain Scale) were performed in the preoperative period (before and after shaving), immediate postoperative, 6, 12, 18, and 24 hours after surgery. The images were analyzed by specific software to define the minimum and maximum temperatures of the region photographed, and these analyses were related to pain scores obtained in each moment. The temperature was highest at 18 hours after surgery. Pain scores presented highest values at 6 and 12 hours after the procedure. There was agreement between thermographic evaluation and pain score 24 hours after surgery, when both parameters reached their lowest values, suggesting that the inflammatory process was decreasing, and that during the other evaluations, it had gotten to its peak. Thermography is an effective method to evaluate the degree of inflammation in the postoperative period of unilateral mastectomy in dogs. When combined with the application of pain scales assessment, it's an efficient tool for pain detection.