The majority of studies was undertaken on large companies that had adopted e-Business or on the specific case of dot.com companies. However, despite this interest in the effect of the size of an organization on its approach to e-Business, little direct comparison has been undertaken between small and large companies. This study examined the differences of e-Business adoption factors and e-Business performance between large and small companies. Reviewing the literature, we suggest a research model and develop nine hypotheses to be tested. Data are collected from 109 companies Implemented e-business. The results of hypothesis testing show as follows. First, e-Business performance of efficiency has a positive influence of perceived e-Business advantage, top management support, organizational learning ability and financial slack. Second, e-Business performance of sales performance has a positive influence of top management support. Third, e-Business performance of customer satisfaction has a positive influence of technology competence, perceived e-Business advantage, top management support, financial slack and institutional pressure. Finally, there are differences in the e-business factors(perceived e-Business advantage, top management support, institutional pressure) and e-Business performance(efficiency) between large and small companies.