The out-of-plane elastic moduli of two polyimides, such as Poly(4,4'-oxydiphenylene pyromellitimide) (PMDA-ODA) with flexible chains and poly(p-phenylene biphenyl tetracarboximide) (BPDA-PDA) with rigid-rod-like chains, ranging from 4 to 20 mu m have been investigated using a precision capacitance dilatometry with a loading-unloading technique. It is found that the elastic moduli of both polyimides in the out-of-plane direction are smaller than in the in-plane direction and they are dependent on the film thickness. In addition, PMDA-ODA is less anisotropic than BPDA-PDA. It indicates that the anisotropy in modulus is dependent on the molecular structure of polyimide. Experimental results show that the out-of-plane elastic modulus is correlated to the in-plane molecular orientation and the main chain structure of polyimide.