Abstract The role of the polishing slurry is crucial in chemical mechanical polishing (CMP) of fused silica (FS). Researching on cycle characteristics of slurry contributes to exploring the deterioration mechanism and prolonging the service time. In this paper, cycle characteristics of colloidal silica slurry and ceria slurry applied in CMP of FS were investigated when the two slurries were recycled for 53 and 42 hours, respectively. The changes of the material removal rate (MRR) and surface roughness (Rq) of FS were analyzed, and the material removal mechanism of both slurries had been discussed. Scanning electron microscopy (SEM) and X‐ray photoelectron spectroscopy (XPS) were employed to interpret the changes of the slurry characteristics. The results indicate that with the increase of recycling time, decrease of pH value and increase of solid content are two common factors which affected MRR improvement for both two kinds of slurries. For colloidal silica slurry, the Rq value fluctuates probably due to unchanged sizes and deformed shapes of SiO 2 . For ceria slurry, the Rq value increases probably due to the size reduction of ceria particles.