A comparative study of polyphenol oxidase (PPO) from two Turkish varieties of quince (Esme and Kalecik) was conducted to determine some of the characteristics of the enzymes in terms of temperature and pH optima, substrate specificity, thermal inactivation and potency of some PPO inhibitors. PPO was partially purified by ammonium sulfate precipitation followed by dialysis. The optimum pH and temperature of the two PPOs were found to be similar The apparent substrate specificity was established from V-max/K-m as 4-methylcatechol > catechol > pyrogallol for PPO from Esme variety (PPOEsme). The substrate specificity for PPO from Kalecik variety (PPOKalecik) was catechol > 4-methylcatechol > pyrogallol. Heat stabilities and substrate specificities of the two enzymes differed.