Single fiber model composites consisting of epoxy resin matrix and differently sized glass fibers were investigated using pull-out tests, scanning electron microscopy (SEM), scanning force microscopy (SFM) and single fiber dynamic load test (SFDL). The inhomogeneous stress distribution along the embedded fiber length could be visualized by monitoring. SEM images showed either cohesive fracture or adhesive failure on pulled-out fibers with different sizings. The crack initiation and propagation were detected randomly and multiply distributed as the inhomogeneous interphase itself and depending strongly on the fiber-matrix model combination. The meniscus region acts as a material inhomogeneity and its appearence depends on the surface free energies of fiber and matrix and on the curing conditions of the resin. SFM in force modulation mode has visualized different interphase thicknesses and gradients of local stiffness. The SFDL test has been shown as a worthful tool for the comprehensive determination of fiber-matrix interaction.