X‐ray diffraction and dielectric measurement have been applied to investigate the phase transition and transport properties ofSr0.56C60O1.5which is obtained by the reaction ofSrCl2withC60anion aquatic solution. The new compound has a similar structure, but different transport properties as compared with metallic Sr‐doped C60. X‐ray diffraction shows that a first‐order phase transition around 100 °C is related to the rearrangement ofSr2+in the interstitial sites of the C60lattice. The step change of ac conductivity near 100 °C is also attributed to the hopping ofSr2+between interstitial sites. The ionic conductivity indicates the possibility of synthesizing superionic conductors based on C60and its derivatives. ©1995 American Institute of Physics.