The poly(hydroxy ether of bisphenol A)-based blends containing poly(acrylontrile-co-styrene) (SAN) were prepared through in situ polymerization, i.e., the melt polymerization between the diglycidy ether of bisphenol A (DGEBA) and bisphenol A in the presence of poly(acrylontrile- co-styrene) (SAN). The polymerization reaction started from the initial homogeneous ternary mixture of SAN/DGEBA/bisphenol A, and the phenoxy/SAN blends with SAN content up to 20 wt % were obtained. Both the solubility behavior and Fourier transform infrared (FTIR) spectroscopy studies demonstrate that no intercomponent reaction occurred in the reactive blend system. Differential scanning calorimetry (DSC), dynamic mechanical analysis (DMA), and scanning electronic microscopy(SEM) were employed to characterize the phase structure of the as-polymerized blends. All the blends display the separate glass transition temperatures (T-g＇s); i.e., the blends were phase-separated. The morphological observation showed that all the blends exhibited well-distributed phase-separated morphology. For the blends with SAN content less than 15 wt %, very fine SAN spherical particles (1-3 mu m in diameter) were uniformly dispersed in a continuous matrix of phenoxy and the fine morphology was formed through phase separation induced by polymerization. Mechanical tests show that the blends containing 5-15 wt % SAN displayed a substantial improvement of tensile properties and Izod impact strength, which were in marked contrast to those of the materials prepared via conventional methods.