The binary and ternary phase behaviors of mixtures of palm kernel oil (PKO), palm stearin (POs), and palm olein (POo) were studied using isosolid diagrams. Both PKO/POs and PKO/POo binaries displayed eutectic behavior at high temperature, while binary POs/POo mixture showed good compatibility and only slight monotectic effect was observed at low temperature in the 10–50% POs addition range. Ternary phase diagrams showed that eutectic effects were observed in all ternary blends at 10–20°C and the degree of interaction depended on the content of PKO, POs, and POo in the blends. The depression of the contours in the isosolid diagrams demonstrated the dominant role of PKO and POo in the ternary system. When the amounts of POs and POo were both 45%, the derivation (ΔSFC) reached a minimum at 10–20°C, which means the weakest eutectic interaction. X-ray diffraction results showed that addition of PKO into the blends could stabilize the β′ crystal whereas the increase of the content of POs would make the blends undergo a β′ to β polymorph state transformation.