A ferroelectric/paraelectric multilayer thin film having a high tuning rate of a dielectric constant and small dielectric loss to overcome limitations of a tuning rate of a dielectric constant and dielectric loss of a ferroelectric thin film, a method of forming the same, and a high frequency variable device having the ferroelectric/paraelectric multilayer thin film are provided. The ferroelectric/paraelectric multilayer thin film includes a perovskite ABO.sub.3 structure paraelectric seed layer formed on a substrate, and an epitaxial ferroelectric (Ba.sub.xSr.sub.1-x)TiO.sub.3 thin film formed on the paraelectric seed layer. The high frequency variable device can realize a RF frequency/phase variable device having a high speed, low power consumption, and low prices and excellent microwaves characteristics.