The gamma/gamma' lattice mismatch in specimens of single crystal superalloy SC16 creep deformed at 1223 K and 150 MPa to a creep strain of 0.5 % was measured by means of X-ray diffraction using synchrotron radiation. The measurements have been performed between room temperature and 1173 K in the both directions parallel and perpendicular to the [001] load axis. At room temperature the gamma/gamma' lattice mismatch measured on the (002) reflection has a positive sign and is larger compared to the mismatch in the non-deformed specimen, while the mismatch measured on the (200) reflection is slightly negative and its value is smaller than that of the non-deformed specimen. In both directions the gamma/gamma' lattice mismatch decreases with increasing temperature.