Intense excimer laser excitation of polyimide film gives transient expansion and the following contraction, permanent swelling. and ablation, depending on excitation wavelength and fluence. Ablation by 248 nm excitation takes place only during the excitation laser pulse, and no debris were observed, while that by 351 nm excitation is brought about after sudden expansion. Permanent swelling was observed only for 351 nm excitation, and distinct differences in expansion and contraction behavior were observed between 248 and 351 nm, excitation. On the basis of the morphological dynamics, it is shown that photochemical and photothermal mechanisms can explain mostly the results obtained by 248 and 351 nm excitation, respectively.