Maleic acid-alt-styrene (MAaS) copolymer with number-average molecular weight [Mbar]n= 2500 was used as a compatibilizer in blends of poly(ethylene oxide) (PEO) and poly(styrene) (PS). PEO with weight-average molecular weight [Mbar]w= 105(PEO100) and two PS samples with [Mbar]w= 9 × 104and 4 × 105, respectively (PS90and PS400, respectively) were used. A depression of the melting temperatureTmof PEO in blends containing MAaS relative to pure PEO and PEO/PS blends was observed. The melting enthalpy ΔHmfor the PEO/PS blends containing MAaS was lower than those of pure PEO and PEO/PS blends without compatibilizer. The crystallization kinetics of PEO and the blends were studied by differential scanning calorimetry (DSC) at different crystallization temperaturesTc. Flory-Huggins interaction parameters χ12for the blends were estimated. Their values are in good agreement with those obtained for similar systems and suggest that the free energy of mixing ΔGmixshould be negative. Polarized optical microscopy shows differences in the macroscopic homogeneity of the blends containing compatibilizer that could be attributed to a compatibilization process.