The degradation characteristics of perfluoropolyether (PFPE) for computer hard disk drive have been investigated. Thermal degradation in PFPE started at $170;^{circ}C$ and it was completed at $450;^{circ}C$. If PFPE was contacted with wear fragment from slider made by $Al_2O_3{cdot}TiC$, the thermal degradation was accelerated by the catalytic Lewis acid degradation. The Lewis acid degradation mainly took placed in methylene oride(fluoride) chain scission as well as methylene(fluoride) and hydroxy end chain. As a result, the degradation reaction accomplished as early as at $300;^{circ}C$. The photo oxidation due to UV exposure on PFPE caused the chain scission in methylene(fluoride), and end chain in PFPE without chain scission in methylene oxide(fluoride) and then the molecular weight of PFPE increased by expected secondary reactions between formed radicals in the photo oxidation.