A method of measuring and calibrating thin-film magnetoresistance was investigated MR signals were detected by a flexible four-terminal electrode that contacted the sample surface in order to reduce induction noise. An hf magnetic field was generated by resonance of a coil wound on a ferrite-core connected in parallel with a capacitor. MR curves were successfully measured in an ac field of 110 Oe p-p, at 1.8 MHz.Calibration was performed by measuring ΔR for homogeneous rotation of magnetization in the sample. This was realized by applying a strong dc field vertically to the ac field. A typical example of the error measurement relative to the calibrated value is +11.2 % for 80 Oep-p at 1.0 MHz.