AbstractFree standing films of blends of poly(ethylene oxide) and natural rubber‐graft‐poly(methyl methacrylate) (PEO/NR‐g‐PMMA) with 40 mol% of PMMA‐graft were prepared at different mass compositions using solution casting technique. These blends show immiscibility in the molten state as indicated by two glass transition temperatures (Tg's), which correspond relatively close to the PEO and NR‐backbone components. The assessment of Tg of the PMMA‐graft can not be made under the experimental condition (heating up to 80 °C). It is expected that the Tg of PMMA‐graft is around 100 °C. Upon cooling from the melt, PEO crystallizes and liquid‐solid phase separation takes place. At room temperature, although the blends are immiscible, results show that the amorphous phase of the blends may comprise of mixture of compatible interfacial region of PEO and PMMA‐graft. Differential scanning calorimetry (DSC) analysis was used for the qualitative assessment of the blend compatibility. The compatibility of PEO and PMMA‐graft was evaluated by change in heat capacity (ΔCp) of the glass transition of PEO and NR‐backbone in the blends. Furthermore, the crystallinity (X*) and melting temperature (Tm) of PEO in the blends at higher content of NR‐g‐PMMA are depressed, which support the Tg and ΔCp results. These findings are in agreement with PEO crystalline structure from WAXS analysis and morphological studies where the PEO spherulites show a significant change upon addition of NR‐g‐PMMA in the blends.