This study investigates the effects of individual and group level factors on the use of GSS (Group Support System) and task performance from GSS use. GSS facilitates the group work, so that GSS adoption is not necessarily influenced only by individual perceptions on information systems as TAM insists. Adaptive Structuration. Theory (AST) joins with TAM in our study to explain the adoption and success from GSS use. AST contends that the success of IS is not necessarily the technical fit between tasks and technology, instead the political outcome among user socializations. We found that collected data from 303 individual IT staffs in a national bank. Our results demonstrate that traditional theories on TAM (Technology Acceptance Model) need to be refined, when considering the TTF(task-technology fit). TTF render high influences on PU(perceived usefulness). PEU(perceived ease of use) and FOA(faithfulness on appropriation). And FOA influences highly on our dependent variable. Implications and directions for future research are discussed.