We demonstrated that demolding in ultraviolet (UV) nanoimprinting was assisted by a nanoscale lubricating fluid layer of a liquefied 1,1,1,3,3-pentafluoropropane (PFP) gas. UV-curable Resin A composed of glycerol 1,3-diglycerolate diacrylate with low PFP absorption showed low surface roughness of 22-nm line-and-space imprint patterns with the smallest line edge roughness (LER) value of 3σ = 1.8 nm. As the molar ratio of 1,6-hexanediol diacrylate with large PFP absorption was increased in the UV-curable resin, the morphological characteristics worsened. Although thin cured films of Resin A possessed a large surface free energy of 57.6mJ m-2 Resin A could be used for step-and-repeat UV nanoimprinting with bare and fluorinated silica molds. Quartz crystal microbalance measurements suggested that a PFP adsorption layer was formed at a film surface of uncured Resin A upon exposure to PFP gas and functioned as a nanoscale lubricating fluid layer during UV nanoimprinting.