Changes of oil contents and fatty acids composition during the development of kernels of Yalova-1 and Yalova-4 walnut varieties were investigated. Samples were taken from trees by 20 days intervals in this period and analysed. Oil contents of cultivars increased as parallel to the kernel development. These increases were statistically significant (P <0.05). Palmitic (16:0) and stearic (18:0) acid contents have decreased as kernels develop. The decreases of palmitic acid contents were statistically significant, but stearic (P <0.05). Oleic (18:1) acid increased regularly and reached maximum level at the harvest date. Linoleic (18:2) and linolenic (18:3) acid contents decreased during the fruit development period. The changes of these acid contents were statistically significant except linoleic acid of Yalova-4 (P <0.05).