Since 2004, eBay has been sued by various famous trademark owners for secondary trademark infringement occurred on its auction websites in United States and European countries. The courts in different countries reached different decisions on the secondary trademark liability of eBay. This paper discusses the principles and factors to be concerned in secondary trademark liability by analyzing three leading cases: Tiffany (NH) Inc. v. eBay Inc., 600 F.3d 93 (2nd Cir. 2010), L'Oréal v. eBay, [2009] EWHC 1094 (Ch), and L'Oréal v. eBay, Case C-324/09 L'Oréal v. eBay [2011] ECR I-0000, together with two EC directives: Directive 2000/31/EC, E-Commerce Directive and Directive 2004/48/EC, IRP Enforcement Directive.This paper also proposes some amendments to R.O.C. Trademark Act after analyzing current R.O.C. Trademark Act, R.O.C. Copyright Act and relevant court decisions and making comparisons with above-mentioned cases and EC directives.