Commercial off-the-shelf (COTS) systems e.g., enterprise resource planning (ERP) system have been adopted by most of enterprises to support the inter- and intra-company business processes. However, research indicated that about three quarters of the ERP projects were judged to be unsuccessful. A common problem confronted when adopting ERP software has been the issue of misfits, that is, the gaps between the function offered by the package and that task requirements by the adopting organization. The type of misfits has been clustered into three categories: data, functional, and output. This paper presents a methodology on the perspective of task-technology fit theory to identify the data and output misfit in the ex-ante evaluation of IS package. With this methodology, the enterprise can more easily and systematically find out where the misfits are and what the degree of misfit is prior to the decision of system implementation.