Utilizing X-ray reflectivity and infrared reflection absorption spectroscopy (IR-RAS), we have investigated the thermal expansion and contraction of ultrathin polyvinylphenol (PVPh) films supported on a silicon (100) substrate capped with an amorphous SiO2layer. Despite being known to form strong interactions with the SiO2surface, the thin PVPh films showed a reduction in the glass-transition point Tg, similar to the behavior of polystyrene thin films deposited on SiO2. We explored the relationship between thermal expansivity and film thickness using well-annealed films and found that it decreases with film thickness in the range below twice the radius of gyration of a polymer chain (2Rg) in the glassy state. Thickness expansion in the glassy state and contraction in thickness at temperatures higher than Tg bulk(melt state) showed the presence of two competing relaxation processes. The reported negative thermal expansion in PVPh thin films, which was discovered to be one of the inherent properties, may have been caused by the fast relaxations that take place at the free polymer surface. IR-RAS was utilized to investigate the effect of thickness on hydrogen bonding in PVPh, and it was confirmed that with decreasing thickness, hydrogen bonding becomes weak, and the number of free OH groups increases. Therefore, thinner PVPh samples exhibit lower Tgs as an effect of easier molecular motions.