Phase transition in lithium manganese oxide spinel synthesized by sol–gel technique and in samples prepared from commercially available powders of LiMn 2 O 4 (Alfa-Aesar and Sigma–Aldrich) was investigated. In addition to the standard impedance measurements and the X-ray diffraction in Bragg–Brentano geometry, simultaneous measurements of impedance spectrum and X-ray pattern in non-focusing geometry were performed in the temperature range between −25 and +100°C. Correlation between the XRD profile parameters and the electrical conductivity was evidenced. Spinel synthesized by the sol–gel technique and heat-treated at 800°C as well as samples prepared from Alfa-Aesar powder exhibited a distinctive phase transition from cubic to orthorhombic structure upon cooling below room temperature. Structural transition was visible in the X-ray pattern as splitting of the 400 reflection of cubic structure, and was accompanied by a decrease of conductivity by a factor of about 10. In the sample prepared from powder supplied by Sigma–Aldrich the phase transition was not complete even upon cooling to −25°C, and no stepwise change of conductivity was observed. Differences in behavior of the spinel samples can be related to the presence of additional phases (Mn 3 O 4 or Li 2 MnO 3 ), which were found in commercial powders, whereas the sol–gel synthesized samples were single phase.