Recently expanded and enhanced software system inevitably demands serious managerial considerations on its maintenance cost. This study proposes a systematic and thorough assessment model for software development methods to the end of maintainability, incorporation ISO 9126 quality standards-based criteria. The Analytic Network Process (ANP) is employed in our model to find the effect of any dependency among the items of the criteria and the alternative methods. This study then applies the model empirically in order to evaluate the efficacies of the Structured Method and the Objected-Oriented Method. At first, this study performs the test on the existence and direction of any dependency under the three types of assumptions, and then determines the relative dominance of the two methods.