Walnut (Juglans regia L.) is the most widespread nut tree in the world, and its production has increased worldwide in the last decade. In the present study, the phytochemical composition and antioxidant activity of 14 superior walnut genotypes in different parts of Kohgiluyeh and Boyer-Ahmad province, Iran were studied. Traits, such as oil, fatty acid profile, antioxidant activity, kernel and oil color, mineral elements, and phytochemical properties were assessed. The results showed that different genotypes have significant differences in terms of investigated traits. The average percentage of kernel oil in different genotypes varied from 36.72 to 63.69%, percentage of protein varied from 13.15 to 21.73%, the flavonoid content varied from 18.67 to 45.79 mg/100 g, the total phenol varied from 76.24 to 932.7 mg/100 g, antioxidant activity varied from 11.25 to 35.49%, and ash varied from 1.49 to 2.14%. The predominant fatty acid was linoleic acid ranging from 50.06 to 68.03%, followed by oleic acid (15.63–35.03%), palmitic acid (8.64–11.93%), linolenic acid (2.2–2.75%), and stearic acid (1.11–2.74%). The highest oil percentage belonged to genotype Setangan-1, and the highest total phenol content was observed in genotypes Setangan-1 and Kowkhdan-2. The highest antioxidant activity was related to genotype Kowkhdan-2, and the highest protein and ash contents were related to genotype Deliraj-2. The genotype Delirej-1 had the highest linoleic acid (68.07%), while the genotype Kowkhdan-2 had the lowest amount (50.06%). The highest content of phosphorus (P), potassium (K), sodium (Na), and iron (Fe) was obtained in genotypes Vezg-2 and Delirej-1, respectively. Hence, genotypes Setangan-1, Kowkhdan-2, Delirej-1, Delirej-2, and Vezg-1 are recommended to be used in walnut breeding programs.
