Fish fat-containing waste is a promising source of lipids used in the microbiological synthesis of biotechnology products. The traditional method of obtaining fat is thermal, based on high-temperature destruction of fat cells. However, only reserve fats are extracted in this way. To increase the degree of fat extraction from fish waste, a combined method was used based on preliminary exposure of fish raw materials to ultrasound followed by heat treatment. The aim of the work was to study the effect of ultrasound on the degree of fat extraction from fish waste and its quality. The objects of the study were waste from fish processing enterprises in the Kaliningrad region: smoked sprat heads, pike perch entrails, and mackerel heads. The yield of fat was determined by varying the ultrasound frequency, temperature and duration of extraction. The acid, peroxide, iodine, thiobarbituric and anisidine values, saponification value, unsaponifiable matter and impurity content at different pH values in the fish-breeding environment were analyzed in the fat samples. A pecularity of the ultrasound effect on fish raw materials is the increased formation of protein-fat emulsion in the extracted fat mass due to the emerging cavitation phenomenon and the increased amount of phospholipids in the fats of fish waste. The emulsion formation decreased the degree of fat extraction by 12.8-17.7% of its content in the raw material. Mathematical models of fat extraction were obtained, based on which the key factors of the thermal stage of the combined process were optimized. It is recommended to extract fat from fish waste using a combined method in two stages with the following parameters: 1 – ultrasound exposure to the fish-breeding mass with a frequency of 40 kHz for 30 minutes; 2 – heat treatment at 83-90 °C for 22-30 minutes. The fats extracted from fish waste using ultrasound are characterized by quality indicators favorable for use as a carbon source in the microbial synthesis of degradable bioplastics – polyhydroxyalkanoates.