Interfacial properties of glycidyl methacrylate grafted ultra-high molecular weight polyethylene fibers and nano clay/epoxy resin were characterized by a microdroplet test. Nano clay (1, 3 and 5 wt%) was dispersed in both acetone and an acetone epoxy solution to form pastes. The X-ray diffraction (XRD) and transmission electron microscopy (TEM) images show that agglomerates of nano clay (1 and 3 wt%) were broken down to form small particles consisting of several clay platelets. The interfacial shear strength (IFSS) of the GMA-grafted fiber/epoxy system has been greatly enhanced with the addition of nano clay. With the addition of only 3 wt% of clay, the IFSS increased by 228.8% up to the original composite. Scanning electron microscopy (SEM) was used to examine the characteristics of the fracture surfaces after the microdroplet test.