A conventional X-ray diffractometer has been used to determine the γ/γ lattice misfit and γ volume fraction for a Ru-containing nickel-based single crystal superalloy at room temperature.The rocking curve was used to characterize the distribution of subgrains.The diffraction peaks obtained by ω-2θ scan were used to determine the γ/γ lattice misfit and γ volume fraction.A three peaks fitting model was proposed.The peak fitting results are in good agreement with the model.The X-ray diffraction results indicate that the nickel-based single crystal superalloy was not a perfect monocrystalline material,which is comprised of many subgrains;and each subgrain also consists of large numbers of mosaic structures.In addition,two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement.The experimental results show that the γ/γ lattice misfit and γ volume fraction will be various at the different regions of its dendritic microstructure.The average γ/γ lattice misfit and γ volume fraction of the experimental alloy are approximately-0.2% and 70%,respectively.Furthermore,the γ volume fraction calculated by atom microprobe(AP) data is also basically consistent with the experimental results. A conventional X-ray diffractometer has been used to determine the γ / γ lattice misfit and γ volume fraction for a Ru-containing single-crystal superalloy at room temperature. The rocking curve was used to characterize the distribution of subgrains. Diffraction peaks obtained by ω-2θ scan were used to determine the γ / γ lattice misfit and γ volume fraction. A three peaks fitting model was proposed. peak fitting results are in good agreement with the model. The X-ray diffraction results indicate that that the nickel-based single crystal superalloy was not a perfect monocrystalline material, which is comprised of many subgrains; and each subgrain also consists of large numbers of mosaic structures. In addition, two anomalous reflection phenomena were found during the experiment and discussed with respect to their occurrence and impact on the measurement. The experimental results show the the γ / γ lattice misfit and γ volume fraction will be various at the different regions of its dendritic microstructure. The average γ / γ lattice misfit and γ volume fraction of the experimental alloy are approximately-0.2% and 70% respectively. Future and the γ volume fraction calculated by atom microprobe (AP) data is also basically consistent with the experimental results.