UV-irradiation is a stress factor for proteins, leading to disruption of their native structure. Test systems based on UV-irradiated proteins are relevant for researchers, as they allow working directly with damaged protein molecules, which can be important when studying the properties and mechanisms of action of various antiaggregation agents. The study of UV-irradiated proteins can also have applied significance, including medical. Here we studied the effect of UV-irradiation on the structural stability of bovine serum albumin (BSA) using differential scanning calorimetry, CD spectroscopy, intrinsic and ANS fluorescence of the protein. The test system based on UV-BSA thermal aggregation at 50 °C was characterized using dynamic light scattering: the order of aggregation with respect to the protein was determined equal to 2, and the protein aggregation stage was rate-limiting. UV-irradiation leads to irreversible destruction of the BSA tertiary structure and to additional rearrangements of its secondary structure, which are partially reversible and affect the aggregation kinetics of UV-BSA. In this case, the protein does not form a "molten globule" and with an increase in the irradiation dose passes into a state of stable small aggregates with a partially preserved secondary structure.