In this article, an amphiphilic oligomeric silane (OS) was synthesized as a coupling agent to improve the interface bonding between resin matrix and glass fiber. The effect of the OS coupling agent on the interface of glass fiber/epoxy resin was studied by contact angle measurement, gravimetric measurements of water sorption, scanning electron microscopy (SEM), energy-dispersive X-ray spectroscopy (EDX), and conductive anodic filament (CAF) resistance test. With the addition of the OS to the composites, the contact angle between epoxy resin and glass fiber decrease notably. Normalized water sorption by gravimetric measurements showed that the interfacial debonding time of composites with the OS can be prolonged significantly. CAF tests were also consistent with the water sorption results, which suggest that the gravimetric measurement of water sorption is a cost-effective method to assess the CAF resistance of materials. © 2011 Wiley Periodicals, Inc. J Appl Polym Sci, 2011.