In this report, the fatigue behavior and lifetime of Polyimicle/silica (PI/SiO2) hybrid films are investigated. To evaluate the fatigue property of this class of hybrid films, the stress-life cyclic experiments under tension-tension fatigue loading with 10 Hz of the frequency are performed, and the stress ratio is 0.1. Dynamic creep and cyclic softening/hardening are analyzed based on the change of hysteresis loops during the fatigue process. The structure-property relations are discussed to further understand their phenomenon and deformation mechanisms. To predict the fatigue life of this class of hybrid films, a semiempirical model is proposed based on fatigue modulus concept. The simulated results are well agreeable with the testing values. (C) 2009 Wiley Periodicals, Inc. J Appl Polym Sci 112: 3276-3283, 2009