In order to develop polarity-modulated hot-melt pressure-sensitive adhesives (HMPSAs), epoxidation of styrene-isoprene-styrene (SIS) copolymers, using in situ prepared per-formic acid was studied. The polymers were characterized with Fourier-transform infrared spectroscopy, H-1 nuclear magnetic resonance spectroscopy, differential scanning calorimetry, and contact angle tests. The epoxidation degree linearly increases with the epoxidation time without side reaction at low temperature. The polarity of the polymers increases with the epoxidation degree. At low epoxidation degree, the 180 degrees peel strength of epoxidated-SIS-based HMPSA increases with the epoxidation degree. In epoxidated-SIS-based HMPSAs, ESIS plays the role of compatibilizer.