This technical report shows a measurement technique for the complex permittivity of a dielectric thin film with the cylindrical resonator having sliding end plates in the millimeter wave region. In order to eliminate the influence of unwanted TM₁₁₁ resonance mode which is frequently appeared on the response of TE₀₁₁ for measurement of the dielectric thin film, the position of the end plates is adjusted adequately. The methodology and experimental results are presented to show the usefulness of this technique.