The dc magnetic field dependence of surface resistance Rs of YBa2Cu3O7-δ (YBCO) thin films were investigated. The YBCO thin films were deposited by co-evaporation method, fabricated by THEVA corp. The Rs of the YBCO thin films were measured by using the dielectric resonator method around 22 GHz and the temperature range below Tc region. The dc magnetic field was vertically applied to the two parallel superconducting thin films. The maximum magnetic field excited by using an NbTi superconducting magnet was 5 T. The Rs values were increased as increasing the applied dc magnetic field. The dependence of the Rs in the YBCO thin films on dc magnetic field was explained qualitatively by Lancaster’s equations for strong pinning limit.