Polyphenoloxidase(PPO) of dog-rose fruit was extracted and purified through (NH4)(2)SO4 precipitation and dialysis. The optimum conditions for this purpose, i.e., pH and temperature, were determined with 4-methylcatechol optimum pH and temperature and found to be pH 8.5 and 20 degrees C, respectively. The inhibition effect of ascorbic acid was investigated and the Iso value was found ta be 1.57 x 10(-4) M. The activity of dog-rose PPO was investigated by electron paramagnetic resonance (EPR) at different pH levels and temperatures. The optimum conditions obtained from both spectrophotometry and EPR were compared.