Pistachios, which are among the top 50 healthiest foods, are rich in antioxidants and are a major source of phenolic compounds known for their related antioxidant benefits. The ripening stage is of paramount importance for food processing since the chemical composition of this fruit is heavily influenced by its level of maturity. For instance, immature pistachios are preferred to be used in desserts, sauces, ice-creams, and chocolate, while mature pistachios are more often consumed as a roasted snack. In this study, the changes in color properties, fatty acids, phenolic compounds, and antioxidant activity at four different maturity periods of the Turkish Uzun pistachio variety were investigated. A total of 13 phenolic compounds were identified and characterized by LC-DAD-ESI/MSn, with a total amount varying between 136 and 210 mg/kg. Catechin, daidzin, and genistin accounted for the highest amount of the total phenolics. The phenolic compounds and antioxidant capacities of the pistachios decreased as the maturation period extended and these two parameters displayed a linear correlation. With regard to fatty acids, Oleic acid had the highest concentration in all the samples, followed by Linoleic and Palmitic acids. The oil yield and fatty acids of pistachio also increased as maturation periods extended in the samples. Practical applications Pistachios have a high nutritional value and many health benefits, with their rich content of phenolic compounds and fatty acids. The ripening period could lead to differences in phenolic compounds and other bioactive properties. The findings of this research could be helpful to determine the optimal maturity index of the pistachios for their usage in specific foods. Thus, it may lead to a decrease in production costs, with use of the most expensive ingredients becoming more efficient.