Animal by-products are whole bodies or parts of animal bodies, products of animal origin or other products derived from animals, not intended for human consumption, including ova, embryos and semen. Their harmless removal is important for the prevention of infectious and parasitic diseases of animals and humans. Therefore, the processing technology of animal by-products is important and will be clarified on the example of the processing technology of the company "Agroproteinka d.d.", which is the largest processor of animal by-products in Croatia. The paper describes the current legislation in the Republic of Croatia related to animal by-products as well as the categorization of animal by-products on which the processing technology itself depends. The paper describes the use of animal by-products and processing technology, then the analysis and quality of production products (meat and bone meal, technical fat, processed animal protein of mixed and poultry material and animal fat). For each of these products, quality parameters are described along with graphical representations. It is important to emphasize the importance of the collection and treatment of animal by-products itself and this is closely related to disease prevention and environmental protection. It was concluded that there is a positive correlation between improper holding of animal by-products before collection and the rate of rot. That is why it is important to improve the system of handling animal by-products until collection.