Mobility of molecularly thin lubricant film is an important issue in understanding boundary lubrication mechanisms and to develop reliable magnetic disk media. Intra-molecular mobility for a perfluorinated poly ether (PFPE), which is used as a disk lubricant, with two hydroxyl groups on a sol-gel SiO2surface, which is used for a protective overcoat for plated magnetic disks, was studied using nuclear magnetic resonance (NMR). Thin film viscosities for molecular segments were derived from a relaxation time. The viscosity for the hydroxyl segment is 1.8 to 11 times as much as that for a bulk lubricant at room temperature, and the viscosity rate increased with increasing temperature. For example, it increased 15 times at 100°C. The viscosities for the segments in a main chain were not different from that of bulk PFPE.