Polyphenol oxidase (PPO) was partially purified from dill by (NH 4 ) 2 SO 4 precipitation followed by dialysis and gel filtration chromatography. Polyphenol oxidase activity was measured spectrophotometrically at 420 nm using catechol, dopamine and chlorogenic acid as substrates. Optimum pH, temperature, and ionic strength were determined with three substrates. The best substrate of dill PPO was found to be chlorogenic acid. Some kinetic properties of the enzyme such as V max, K M and V max /K M were determined for all three substrates. The effects of various inhibitors on the reaction catalysed by the enzyme were tested and I 50 values calculated. The most effective inhibitor was L-cysteine. Activation energies, E a , were determined from the Arrhenius equation. In addition, activation enthalpy, DH a , and Q 10 values of the enzyme were also calculated.