Two commercially available amine-cured epoxy resin formulations were studied under different environmental conditions with regard to the surface tension evolution using axisymmetric drop shape analysis (ADSA). By employing a new strategy, ADSA was used to monitor simultaneously the surface tension and the density of these reactive mixtures from sessile drops. The kinetics of the bulk reactions were quantified by Fourier transform infrared (FTIR) spectroscopy, and the changes in the molecular composition of the surface region were studied by X-ray photoelectron spectroscopy (XPS). In both formulations, the surface tension values of the amine hardeners were lower than those of the epoxy resins. For one system, the surface tension of the mixture was similar to the surface tension of the hardener. In this case, the hardener migrates to the surface and determines the surface tension of the mixture, as could be proved by XPS measurements. In the other case, the surface region contained only a very small amount of nitrogen, indicating that the nitrogen-containing groups of the hardener were not enriched in the surface region of this mixture. Its surface tension was similar to that of the pure epoxy resin. In a controlled argon atmosphere, the surface tension of the reactive epoxy-amine systems considered here changed very little as the curing reaction proceeded. The time-dependent changes of the surface tension of the mixtures were caused by environmental factors, particularly the presence of carbon dioxide and water. Such factors can produce complicated surface tension responses due to surface reactions with the amine hardener. The extent of these changes can be controlled by the migration of the hardener to the surface region.