The aggregation induced by the increased surface pressure of aliphatic coumarin dye molecules in a Langmuir monolayer has been investigated with the aid of surface pressure, UV-Vis 45° angle and Brewster angle reflectometry as a function of the total surface area. The dynamic properties of the structural changes were recorded as compression speed and temperature-dependent shear viscosity and dynamic elasticity of the coumarin monolayer. A sequence of compression-induced phase and structural changes were found as a function of the compression. These changes are related to the formation of H-aggregates which was dependent on the duration and number of the compression-expansion cycles. A simple model is offered to explain the main aggregation equilibrium of the 7-aminocoumarin molecules. The compression-induced structure was dependent on the compression speed, the temperature and the dilution in a stearic acid matrix.