Conceptual structural design of the main wing for the 20 seats WIG(Wing in Ground Effect)flight vehicle, which will be a high speed maritime transportation system for the next generation in Rep. of Korea, was performed[1,2]. The high stiffness and strength Carbon-Epoxy material was used for the major structure and the skin-spar with a foam sandwich structural type was adopted for improvement of lightness and structural stability. As a design procedure for this study, firstly the design load was estimated through the critical flight load case study, and then flanges of the front and the rear spar from major bending loads and the skin structure and the webs of the spars from shear loads were preliminarily sized using the netting rule and the rule of mixture[4,5]. In order to investigate the structural safety and stability, stress analysis was performed by commercial Finite Element code such as NASTRAN/PATRAN. From the stress analysis results, it was confirmed that the upper skin structure between the front spar and rear spar was weak for the buckling. Therefore in order to solve this problem, a middle spar and the foam sandwich structure at the upper skin and the web were added. After design modification, even thought the designed wing weight was a little bit heavier than the target wing weight, the structural safety and stability of the final design feature was confirmed. In addition to this, the insert bolt type structure with six high strength bolts to fix the wing structure at the fuselage was adopted for easy assembly and removal. As well as consideration of the fatigue limit load for more than 20 years fatigue life.