Mathematical algorithms of the Multiple Attribute Decision Making (MADM) have been applied for well-structured problems. However, they are not appropriate for semi-structured or unstructured problems because all the attributes should be transformed into a commonly comparable and quantitative scale. Thus, it is apt to miss the domain expert``s qualitative knowledge which can not be neglected. The problem of military weapon system acquisition is composed of both quantiative and qualitative attributes. Those attributes such as performance/effectiveness of the weapon system may be quantified. On the other hand, it is not easy to quantify certain attributes such as technology status and economic factors. Therefore, it is more natural to consider such factors in qualitative form. This thesis therefore proposes a framework for weapon acquisition decision and develops a prototype for WASS (Weapon Acquisition decision and develops a prototype for WASS (Weapon Acquisition Support System) which considers both quantitative and qualitative attributes. For the quantitative attributes, a modified Simple Additive Weighting (SAW) method is applied. For the elicitation of weights, the Analytic Hierachy PRocess (AHP) method is used. The qualitative attributes are represented in rules. In addition, the technology evaluation is represented in semantic net to support the inheritance property among technology areas. We have demonstrated that the results by WASS is more natural and easy to use than those by the purely quantitative SAW approach.