Although data about the importance of pistachio in human nutrition has extensively increased in the last years, the fruit physical and chemical characteristics of some Iranian pistachio cultivars during fruit ripening have not been evaluated in detail, yet. Thus, the investigation of physicochemical properties and antioxidant activity of four pistachio cultivars (‘Akbari’, ‘Kalleghoochi’, ‘Ohadi’ and ‘Sephid’) at ten different developing stages, from 11 June to 9 September (10 day intervals), was the aim of the present study. The fresh weight, length and diameter of different cultivars fruit increased significantly throughout fruit maturity and reached the maximum values at last harvesting stage. The shell splitting, early splitting and hull cracking were started since the 6th (31 July), 5th (21 July) and 6th (31 July) sampling dates, respectively. The mentioned parameters significantly showed an ascending trend in all cultivars since above times until the end of the harvesting period. The blank percentage decreased significantly from 4th (11 July) sampling date to the last date of harvesting for all cultivars. Significant decreases in total phenolics, total tannins, condensed tannin and antioxidant activity occurred with the advance in fruit development for all cultivars. Our results provide important information on the changes in physical and chemical properties of pistachio during fruit growth and maturity, which is very useful for determination of the fruit quality. Also, statistically significant differences were observed between different cultivars investigated in all parameters measured. Overall, the kind of cultivar and date of harvest are the important factors determining the physical characteristics, chemical composition and antioxidant activity in pistachios

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