Phase stability and thermal expansion of metastable rs-Me 1-x Zn x O solid solutions at ambient pressure have been studied by high-temperature synchrotron X-ray diffraction at the B2 powder diffraction beamline of the DORIS-III storage ring (HASYLAB-DESY). Debye-Scherrer geometry with rotating quartz capillary was used. The X-ray diffraction patterns were collected in the 10-70° 2θ-range for 2 min in real time using the OBI image plate detector. A NIST powder LaB 6 (Pm-3m, a = 4.15695 Å) was used as standard sample for detector adjustment at 298 K. The furnace temperature was kept constant within 1 K using a Eurotherm temperature controller and Pt10%Rh-Pt thermocouple. The temperature calibration of the setup was performed using well-established reference points: CsCl solid state phase transition (Pm-3m → Fm-3m, 743 K), CsCl melting (919 K), KCl melting (1044 K) and NaCl melting (1074 K). Each following temperature point was set by increasing the heater power. The temperature step was 50 or 100 K. Before each data collection the sample temperature was stabilized for 2-3 min. The diffraction data were analyzed using DatLab software , and positions of diffraction lines were determined by fitting to the Pearson profile function. The lattice parameters were calculated by the least squares method.