The doctrine of equivalents is one of the most difficult and unpredictable doctrines in patent law to apply. By allowing patentees to gain exclusive right beyond the literal claims in their patents, this doctrine creates tension between the adequate protection of patent right and the public notice function in the patent system. The Supreme Court and the Intellectual Property Court in Taiwan continuously apply the interchangeability test to determine the infringement under the doctrine of equivalents. This article reviews the related US and Taiwan case, and the Guideline for Patent Infringement Analysis proposed by Taiwan Intellectual Property Office. Especially, by using the methodology of comparative law, this article provides some comments and suggestions on the interchangeability test applied in Taiwan. Finally, the article concludes that the interchangeability test is not appropriate to determine the infringement under the doctrine of equivalents under some conditions.