A series of CH3NH3PbI3/polyimide (PI) composite films were successfully fabricated using simple solution mixing. CH3NH3PbI3 particles were evenly dispersed into PI substrate, which could be seen from scanning electron microscopy images. Tensile test showed that the tensile strength of CH3NH3PbI3/PI composite film (5 wt%) was improved to the maximum (102.2 MPa), 127% higher than pure PI; and the elongation at break was remarkably stretched to 13% for CH3NH3PbI3/PI composite film (3 wt%), 171% greater than pure PI. Moreover, the thermal performance was enhanced to the optimum with the addition of 5 wt% CH3NH3PbI3. Ultraviolet–visible absorption curves revealed that the colors of CH3NH3PbI3/PI composite films were darkened and the red shift increased with the increasing content of CH3NH3PbI3. Furthermore, the CH3NH3PbI3/PI composite films exhibited increased dielectric constant with the maximum value of 13.8, compared with pure PI (3.6). These composite films may be promising to be used as dielectric materials in electronic industry.