Mechanical and thermal properties of a hot-melt adhesive made of styrenic triblock copolymer, polystyrene-block-poly(ethylene-co-propylene)-block-polystyrene] (SEPS), tackifier and plasticizer were examined in terms of the effect of addition of a homopolymer, poly (2,6-dimethyl 1,4-phenylene ether) (PPE), which is miscible with the styrene component and has the glass transition temperature, Tg (~165°C), higher than that of the styrene component (~90°C). Various methods were applied to examine the properties: atomic force microscopy, shear adhesion failure temperature, 180° peel, dynamic mechanical analysis, and temperature-modulated differential scanning calorimetry. The microscopy indicated a micro-phase separated structure. It has been confi rmed that the adhesive properties depend on the Tg of the styrene domains, which linearly increases with the added content of PPE. Broader glass transition with the addition of PPE indicated the inhomogeneous distribution of PPE in the styrene domains. The heat resistance of the adhesive is sustained by the physical crosslinks made of the glassy styrene domains, which are fi nally broken down above the Tg of PPE-rich core of styrene domains.