The morphology of silk fibroin/poly(vinyl alcohol)(PVA) blend films was investigated using optical microscopy and confocal laser scanning microscopy. The effects of blend ratio and molecular weight of silk fibroin and PVA on phase separation were studied. Macro-phase separation occurred for the silk fibroin-rich/poor region whereas micro-phnse separation took place for the djspersed/continuous phase. In spite of differences in molecular weight and blend ratio, it is obsewed that the dispersed phase and continuous one are composed of silk fibroin and PVA component, respectively. As the molecular weight of silk fibroin and silk fibroin content in blend ratio are decreased, the compatibility of blend films is increased due to the reduction of micro-phase separation.