The mechanisms of intermolecular protein complex formation were studied by the example of monomers, oligomers and aggregates of bovine serum albumin (BSA) depending on the protein concentration, pH and urea concentration. Using dynamic light scattering (DLS), analytical ultracentrifugation (AUC) and PAG electrophoresis, we have shown that there is dynamic equilibrium between monomers and aggregates in BSA solution. Decreasing pH of the solution (4.0—1.0) resulted in increasing sizes of the aggregates. In the solutions with low urea concentrations (below 2 M), the sizes of aggregates decreased, while higher urea concentrations induced formation of larger aggregates due to the unfolding of the protein.