Dielectric films of Bi2WO6 (BWO) more 12.5-nm thick are formed epitaxially on Nb-doped SrTiO3 substrate by pulsed laser deposition (PLD). BWO film shows an atomically smooth surface with a flat terraces of 200-300 nm wide, and steps of 0.8 nm or 1.6 nm, corresponding to one or one-half unit cell. At film thickness of less than 70 nm, the dielectric constants of BWO film are held to a value of 20. A BWO film, with its atomically-flat surface and its dielectric constant (epsilon(r)) unchanging with film thickness, is an ideal material for device applications in the semiconducting field.