Pistachio nuts (Pistachia vera L.) variety Halapy, Family Anacardiaceae were obtained from “Aleppo City", Arab Republic of Syria. The investigated pistachios were kept in perforated standard carton boxes of 45 × 30 × 12 cm dimensions, under a good ventilation conditions. They were irradiated at the National Centre for Radiation Re-search and Technology (NCRRT) at “Nasr City", Cairo, Egypt. Irradiation treatments were applied using Cobalt – 60 facilities “Egypt Mega Gamma 1" model AECL 6500 and the dose levels were 250, 500, and 2000 Gy. The irradiated samples were stored at 20°C for 6 months through which the activities of peroxidase (POD/EC. 1.11.1.7) and pectin methylesterase (PME/EC 3.1.1.11) were followed. The kinetic parameters in terms of Km, Vmax., angle of activity, catalytic efficiency, slope of activity and inhibition levels were considered within a storage period of 6 months. Amino acids and fatty acids profiles of irradiated pistachio were also given. Experiments proved the preference of a dose 500 Gy for inhibiting both of the two tested enzymes in the investigated pistachios during the whole period of storage.