The effect of interfiber distance on the interfacial properties in E-glass fiber/epoxy resin composites was investigated using single and two fiber fragmentation test specimens with various interfiber distance. In addition, the effect of the fiber surface treatment on the interfacial properties was studied. As a result, we found that the interfacial shear strength increased with the increasing interfiber distance in the range between 0 and 50 $mu$m regardless of sized and desized fibers. It was seen that the interfacial shear strengths were in close agreement with those of the single fiber fragmentation test. We also found that when the interfiber distance became smaller, the stress distribution pattern was similar to that of a single fiber and when the interfiber distance became more than 50 $mu$m, the stress distribution pattern was independent of the distance between fibers. Finally, the interfacial shear strength evaluated using two E-glass fiber/epoxy resin fragmentation test is shown as real values in-site regardless of the fiber surface treatment and interfiber distance.