Polyimides (PIs) are considered to be one of the most important engineering materials. Much work has been on their organic-inorganic hybrid fabrication process and the related properties at room and elevated temperatures. However, few results were ever involved in their low temperature properties. In this study, PI/SiO2 nanocomposite films were prepared via sol-gel reaction. The coefficient of thermal expansion (CTE) with different silica contents was measured from room temperature to low temperature (77K) and the possible influence of the applied stress level on CTEs was also considered. It is found that CTEs increase at first, then decrease with increasing of silica contents. Another interesting result is that CTEs have a little decrease as the increase of the stress level, though the change is very little in our study. Moreover, the related mechanical properties of PI/SiO2 nanocomposite films (Ultimate tensile strength, Young's modulus and Elongation at break) at room temperature and low temperature (77K) were also reported to give a comparison.