Total phenol, phenolic compound, total oil, fatty acid, protein contents of walnut kernels from nine different cultivars and six genotypes grown in the USA were investigated. Total phenolic content was found to range from 540.08 to 1067.81 mg GAE/100 g dw, with three cultivars containing a value of or over 1000 mg GAE/100 g dw. A total of seven phenolic compounds were quantified, and their quantity were greatly varied among the cultivars/genotypes. Ellagic acid was the most abundant phenolic compound, varying from 20.03 to 97.23 mg/kg. Total oil component ranged from 53.17% to 65.92% with an average value of ca. 60%. As a saturated fatty acid type, myristic, palmitic, stearic, and arachidic acid; as an unsaturated acid type, linoleic, linolenic acid, oleic, and palmitoleic acid were quantified. Palmitic acid was the predominant saturated fatty acid compound and ranged from 5.74% to 9.49%; linoleic acid was the predominant unsaturated fatty acid compound and ranged from 58.96% to 66.07%. Protein content percentage was notably varied among cultivars and genotypes, ranging from 13.57% to 25.72% with an average value of ca. 21%. These results indicate that the walnut kernel is a good source of fat, phenolics, and proteins, and its abundance are greatly cultivar/genotype-dependent.