In this article, the effects of atmospheric plasma treatment on the microstructural, chemical, and mechanical behavior of epoxy-bonded polycyanurate composites are investigated. Adhesive bond strength of plasma-treated specimens exhibited strength increases of over 35% to that of peel-ply and solvent-wiped surface preparation techniques. The improvements were as much as 50% greater than those obtained using abrasive surface preparation techniques. X-ray photoelectron spectroscopy analysis showed an increase in the surface concentration of oxygen as a function of plasma treatment passes. However, the levels were substantially lower than that of epoxy composites treated under identical conditions. In addition, the concentration of carboxyl groups (O-C=O), which have been associated with improved adhesive strength in epoxy-based composites, was shown to saturate in cyanate ester composites after a much lower exposure period than what was observed when treating epoxies. The effect of plasma surface treatment on the surface morphology of the cyanate ester composite was also studied using scanning electron microscopy and atomic force microscopy. Atomic force microscopy analysis showed a progressive increase in surface roughness with treatment; however, this increase only translated into a marginal increase in surface area and is not believed to contribute significantly to adhesive strength. (C) 2010 Wiley Periodicals, Inc. J Appl Polym Sci 120: 921-931, 2011