The increasing demand for doing business online calls for higher business interoperability on e-marketplaces (EMp). This drives the development of integration technologies for improving EMp functions. This paper argues that by comparing the cost of business interoperability on EMp brought by the integration technology, firms will more favour joining in public EMp than self-building private EMp. In this shift, three integration factors of standard flexibility, service provision and semantic integration are constantly improving EMp functions, which lead to an overall reduction of interaction cost for business interoperation. This will change business behaviours and corporate strategies of most firms and have important implications for firms to make strategies of how to treat EMp to increase business interoperability. © 2008 by Springer Science+Business Media New York.