As in other polymer blends, the phase behavior of silk fibroin (SF) blends with other polymers is thought to be important for their related properties. Here we used FTIR imaging to study the phase behavior of three silk protein-based polymer blends, silk fibroin/chitosan (SF/CS) blend, silk fibroin/sodium alginate (SF/SA) blend, and silk fibroin/polyvinyl alcohol (SF/PVA) blend. FTIR images of the films prepared from these polymer blends indicated that the SF/CS blend was compatible, the SF/SA blend was partially compatible, and the SF/PVA blend was incompatible. The results accord with the conclusions from the conventional analysis methods like SEM, DSC, and DTMA reported in the literature. Moreover, we show that FTIR images of the blends can provide additional useful information on the composition of the individual components, and the conformation of SF at defined locations with a spatial resolution of 4 mm. Therefore, we believe FTIR imaging is a useful technique to better understand both the chemical and physical properties of silk protein-based polymer blends, and other kinds of polymer blends.