The effect of surface treatment on the interphase morphology of liquid crystalline copolyester/ glass fiber (LCP/GF) composites has been investigated by polarized light microscopy (PLM), scanning electron microscopy (SEM), differential scanning calorimetry (DSC), and wide-angle X-ray diffractometry (WAXD). The main objective of this study was to identify the role of fiber in the formation of microstructure and morphology of the composites, particularly its influence on the anisotropic nature of LCP. Two coupling agents, gamma-methacrylate propyltrimethoxysilane (gamma-MPS) and phenyltriethoxysilane (PTS), were employed for the surface treatment of GF. The former reacted with the LCP; the latter did not. "Model composites" were prepared by embedding a single glass fiber in the LCP melt under mechanical shearing between glass slides at elevated temperatures. Experimental results from PLM and SEM revealed a parallel-to-GF LCP orientation at the interface for the composite with no coupling agent, a perpendicular-to-GF LCP orientation for the composite with gamma-MPS, and a random LCP orientation for the composite with PTS. Factors affecting; the formation of these interphase morphologies were analyzed; these facto;rs included (1) the mechanical shearing, (2) the guiding, anchoring, and packing effects of GF, and (3) the interfacial modification by gamma-MPS due to the occurrence of transesterification. The relative importance of the above factors was compared. The above effects of GF were confirmed by comparing the as-sheared and the annealed LCP composites. The occurrence of transesterification was further supported by DSC data which showed a low-temperature transition peak at 224 degrees C in addition to the k-n transition peak. WAXD results indicated almost no change of LCP crystalline structure in the presence of coupling agent, possibly due to the large difference in molecular size of the LCP and coupling agent.