Abstract
To properly define relevant market in terms of antitrust law, this article sorted out available methods brought by economic theory and antitrust law, such as cross-elasticity of demand, hypothetical monopolist test, diversion ratio and SSNIP. To define whether with the like-products sold on Internet is substitutes, this article introduced Brand Performance Measurement as criteria to exam it. This article also introduces the problems as we apply two-sided market theory when defining relevant market. We also would take electronic commerce with two-sided market characteristics as an example to illustrate the limits of SSNIP and how to go around the limits with the methods we bought as we try to define the relevant market with respect to the electronic commerce.