A structural sizing tool in conjunction with the FEM code Nastran was developed to predict wing structural weight of a subsonic aircraft. The tool has a capability to efficiently perform the sizing process with several features including automatic meshing, setup for the optimization problem and analysis job management. Additionally, to save computational cost, buckling strength criterions of theoretical analysis method were introduced as a constraint of the optimization problem instead of the full buckling simulation. The result of a test case is presented and compared with the empirical weight prediction method. The present method shows comparable result with the empirical method than the result without consideration for the buckling related criterions.