This study was conducted on pistachio trees (Pistacia vera L., cv Siirt) grafted on four different rootstocks (Pistacia atlantica Desf., P. khinjuk Stocks, P. terebinthus L. and P. vera L.) to elucidate effects of the rootstocks in the fat content and fatty acid composition of early harvested green pistachio kernels. Fat content and fatty acid compositions were determined after harvesting. The fat content of pistachio kernels ranged from 24% on P. terebinthus to 35.4% on P. atlantica. The fatty acid compositions ranged from 10.83% on P. atlantica to 12.17% on P. khinjuk in saturated fatty acids (SFAs); 68.29% on P. khinjuk to 70.09% on P. atlantica in monounsaturated fatty acids (MUFAs) and 18.42% on P. vera to 19.54% on P. khinjuk in polyunsaturated fatty acids (PUFAs). The unsaturated/saturated fatty acid ratio varied between 7.22 and 8.23. In the present study, we found that the fatty acids were affected by the rootstock in pistachio trees.