Investigation of a spread monolayer of dipalmitoylphosphatidyl glycerol (DPPG), a simplified model of biocell membranes, on the surface of solutions of macromolecules of different surface activity can provide additional information on the processes in cell membranes and, on the other hand, can help in the development of biocompatible materials. In this work, the interactions of β-lactoglobulin (BLG) and its fibrils with a lipid monolayer on the surface of an aqueous solution or a fibril dispersion were studied. The surface layer structure and the ability of macromolecules to penetrate a lipid monolayer depend on electrostatic interactions, the surface activity of the macromolecules, and the packing density of the lipid monolayer. The charged lipid monolayer reduces the adsorption barrier for oppositely charged macromolecules and aggregates, leading to an increase in the adsorption rate and an increase in the surface fibril concentration. The interactions between the lipid molecules and fibrils at the biocell surface can cause the accumulation of fibrillar aggregates there. On the other hand, the interactions between surfactants and fibrils at liquid-fluid interfaces, leading to the formation of thick multilayers, can improve the stabilization of foams and emulsions.