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We have studied electromagnetically induced transparency (EIT) in the 5S_1/2−5P_3/2−5D_5/2 ladder-type system of Rb. We observed relative changing magnitude of EIT hyperfine structures depending on not only the polarizations of the lasers but also the intensity of the coupling laser. The coupling-intensity effects are attributed to the nonlinear increase of the EIT signal to the coupling intensity. EIT signals nonlinear on the coupling intensity are analyzed by considering coherent interaction between atom and laser fields.