An embedded single filament test using aramid fibre has been carried out, not only in tensile mode but also in compressive mode. In the tensile test, all single filaments embedded under various pre-tensions are not fractured until the specimen's break, so that embedded single filament tensile test was not suitable for an evaluation method of the aramid/epoxy interphase. In the compressive test, optical microscope observations indicate the dark zone of/around the embedded single filament after testing. As compressive stress increases, a kink band is generated at first, then kink bands are immediately developed all over the length of the filament and the field becomes clearer. The dark zone first appears after the plastic deformation of the specimen. The intensity of the dark zone measured by image analysis for the micrographs has a linear relationship with the transverse tensile strain which is measured by two strain gauges on the specimen. These results suggest that the dark zone is due to damage of the interface by the transverse tensile strain under longitudinal compressive stress to the specimen. This suggests that it is possible to evaluate the interfacial properties by the measurement of the intensity and the aspect of the dark zone at a constant transverse tensile strain.