MoO3-P2O5 glasses were prepared by a simple melt quenching method. XRD and DSC investigations confirmed the amorphous state of 60Mo-40P, 70Mo-30P and 75Mo-25P glass. Interestingly, HRTEM images revealed the inherent crystallization behavior in Mo enriched glass. The existing nanocrystals performed a synergetic effect with the glass matrix to relax the stress caused by Li ions insertion/extraction. As a result, 75Mo-25P glass with distinct nanocrystals showed excellent long cycling stability. The structural transition of MoO3-P2O5 glass and the valence change of Mo ions during cycling were discussed. Furthermore, CV and EIS measurements were performed to elucidate the difference of redox reaction, electrons transport and ions diffusion in 75Mo-25P glass and crystalline MoO3. This study provides an avenue to exploit new cathode materials with long cycling life for Li-ion batteries.