Monitoring the reaction of an aromatic diamine cure agent with epoxy by fluorescence technique was used for cure characterization of the interphase in epoxy/glass and epoxy/carbon composites. The effect of the various surface treatments was first studied by the model interphase obtained by using a quartz plate for glass or a modified quartz plate for carbon surface. Aminosilane treated quartz cured faster and showed increased cure extent, while water aging and air oxidation showed almost no effect on the cure kinetics in comparison to the untreated quartz surface. For a model carbon surface, air oxidation showed a faster reaction only at the early stage of cure. The effects of the various surface treatments on glass or carbon fiber were also studied with the actual composites made by a thin coating of epoxy-diamine melt on glass or carbon fiber bundles. Epoxy/glass fiber composite showed a similar trend as the model interphase system. In the case of epoxy/carbon fiber composite, both air oxidation and water aging treatment showed a faster cure reaction at the early stage of cure. Furthermore, air oxidation treatment for the epoxy/carbon fiber composite showed somewhat increased cure extent. The reasons for these trends have been discussed.