Since aramid fibers have very high crystallization degree and high chemical inertness, the surface modification is needed to enhance the adhesion between fibers and matrix for the usage of composite applications. In the present study, para-aramid fibers were treated by atmospheric pressure plasma under various plasma powers to improve interfacial adhesion between aramid fiber and epoxy resin. The surface morphologies of untreated and treated fibers were investigated by scanning electron microscopy (SEM) and Fourier transform infrared (FTIR) spectroscopy. Composite interfacial adhesion properties were determined by interlaminar shear strength (ILSS) using a short-beam bending test. Results indicated that argon plasma treatment was an effective method for improving interfacial adhesion between fiber and matrix with ecological treatment.