The surface of polymers is believed to have high mobility, and their glass transition temperature decreases significantly from the bulk value. In this study, we prepared a molecularly flat poly(methyl methacrylate) (PMMA) substrate by thermal nanoimprinting a PMMA plate with an atomically stepped sapphire substrate. The imprinted PMMA surface with a step height of ca. 0.2 nm was stable for months in air at room temperature and was retained even after immersion in water for 10 h. PMMA chains and an isotactic PMMA crystalline monolayer deposited on the imprinted PMMA substrate by the Langmuir-Blodgett technique were observed by atomic force microscopy at the molecular level, and the molecular structures were stable for months in air at room temperature. These significant stabilities of the surface of the imprinted PMMA substrate and the monolayers deposited are unexpected and differ from the results expected based on our present understanding of the polymer surfaces. The results indicate that the properties of the thermally pressed polymer surface may be different from those of the previously studied solvent-cast polymer surfaces.