Knowing the time of death of animals can be helpful for the forensic determination of death due to cruelty. We aimed to determine the time of death of companion animal carcasses, euthanised at an outpatient’s department (Small Animal Clinic) of the University of Veterinary Medicine and Pharmacy in Kosice. The reasons for euthanasia included age of animals, medical state or incurable disease which affected the quality of life. Animal carcasses (33 bodies) were divided into seven groups according to their weight, species and environmental conditions into which they were placed, which were chosen so as to imitate real conditions under which dead animals could be found. We continually measured body temperature until it dropped down to ambient temperature. The post-mortem cooling curve revealed dependencies related to the temperature drop, the weight of carcasses, the place where animals rested and the internal and external environment. Results from the cooling process and obtained time of death may be deduced from a nomogram in field practice.