The objective of the research study was to optimise the process of thermal sterilisation of canned fish products on the basis of the determination of temperature distribution in water-spray autoclaves. Tested were retorts used under the industrial production conditions of canned fish. The first stage of the optimisation process is to study  the temperature distribution in industrial autoclaves. At this stage, the temperature field is determined in the  inner space of autoclave vessel with the product-filled sterilisation baskets. It is necessary to determine the slowest heating autoclave zone in order to further conduct heat penetration tests in canned fish and thus to determine the  minimum duration times of sterilisation at a set temperature so as to reach a level of safe (microbiologically)  sterilisation value of F₀ for the minimum 3 min. The F₀ symbol is an assumed unit of operation of 121 ºC  reference temperature during the given time of thermal sterilisation process and it is an indicator to determine the effectiveness of inactivation of microorganisms. During the temperature distribution analyses, there were  compared the duration time of inner space heating in individual autoclaves to the true sterilisation temperature  set in the coldest point of a given vessel depending on the initial temperature of canned fish. Also the temperature distribution was compared in the individual autoclaves after the 1, 3 and 5 min of the true  sterilization. The temperature distribution analyses were conducted in nine different autoclaves and their results  proved that the time needed to reach a true sterilisation temperature ≥ 115 ºC was 17 to 23 min. This means that a minimum time of 23 min is required for the heating stage duration under the industrial production conditions, where it is necessary to organisationally optimise the sterilisation procedure and to establish one sterilisation  process pattern for several autoclaves. Thus the basic objective of the heat sterilisation process is to ensure  microbiological safety of a food product having regard to the most difficult conditions of heat exchange during the  process.