The complex permittivities of methanol measured from 0.2 to 2.0 ㎓ using an open-ended coaxial probe revealed the large deviation from the given data in literature. In this paper, it was investigated whether the given or measured complex permittivity is similar to the real value of our methanol used for experiment. The FDTD method was applied to confirm the effect of our conversion model excluding the effect of sufficiently small measurement error. The complex permittivities reconverted from the computed reflection coefficient by employing our improved conversion model were not similar to the given value but measured value. These results assured the accuracy and stability of our measurement-and-conversion process.