Aggregation states of polymers at the surface generally tend to alter to their most stable ones in response to their surrounding environment. We here apply a time-resolved contact angle measurement to examine the rate of the surface reorganization of poly(methyl methacrylate) (PMMA) in water. By doing these measurements at various temperatures, it is possible to extract the apparent activation energy of the surface dynamics based on the relation of the surface relaxation time and temperature. Also, sum-frequency generation spectroscopy revealed that the surface reorganization involves the conformational changes in the main chain portion as well as the side chains. Hence, the dynamics observed here might reflect the segmental motion at the outermost region of the PMMA film, in which water plays as a plasticizer.