Photo resist thin films have mainly been used and investigated for versatile applications of micro electronic mechanical systems because of its outstanding aspect ratio and attainable film thickness. An accurate structure properties derived from validated material characterization is required in engineering applications. In this work, dynamic responses of photo resist thin films are tested by a nanoindentation in association with a dynamic mechanical analysis, where the thin film is coated on a silicon wafer by spin coating. The results show that the storage modulus of the photo resist thin film remains constant at the beginning and then increases as the indentation depth increases. Meanwhile, the loss modulus increases as the indentation depth increases. Varying the film thickness shows that the substrate effect plays an important role in determining the dynamic properties of thin films. However, the results agree well with the bulk material when the amplitude of nanoindentation is relatively small. It illustrates the dynamic mechanical analysis can be an efficient method to characterize the viscoelastic properties of thin films, but proper attention on the test parameters is needed.