Various treatments were used to determine polyphenol oxidase activity changes during osmotic dehydration of banana slices. A temperature of 35 °C and 5.0 pH were used as the most adequate conditions for polyphenol oxidase activity determination when 4-methyl catechol was used as a substrate. Enzyme activity change was determined in the central and edge region of fruit. The central part of the banana slice showed 2.4 times higher activity than in the edge region. A difference in the kinetics of enzyme activity decrease also occurred during four hours of drying. When the drying was carried out at 70 °C, the enzyme was completely inactivated after 60-90 minutes of specific osmotic treatments. After four hours of osmotic drying at 50 and 60 °C, polyphenol oxidase activity was still present; the residual activity varied from 1.3 to 15 %.