Changes in the structure of single-crystal (SC) superalloy SRR99 during creep at 980 degreesC and 200 MPa were investigated. Geometrical. parameters of the gamma/gamma ' -microstructure, gamma/gamma ' -misfit, stresses in the phases and local misorientation of the structure were determined at defined points of the dendritic structure by use of X-ray diffraction (XRD), wavelength dispersive X-ray spectroscopy (WDXS), scanning (SEM) and transmission (TEM) electron microscopy. Correlation of the microstructural period and local misorientation of the structure with creep strain were found.