An X-ray imaging plate system has been applied for the first time to evaluate the crystallite modulus E(c) of orthorhombic polyethylene along the chain axis. The E(c) evaluated by using the 002 reflection was 234.9 +/- 12.6 GPa and that for the 004 reflection was 236.7 +/-3.4 GPa. The dispersion of the data was smaller for the 004 reflection than that for the 002 reflection. The so evaluated modulus has been found to be in good agreement with that reported by previous researchers.