With the increase in international exchanges, international criminal activities follow the increasing trend without exception. Law enforcement agencies are trying hard to cross the boundaries to obtain evidence abroad. Among these cross broader actions, gathering evidence abroad under international mutual legal assistance and the role of such evidence in criminal procedure, have been studied by scholars from different perspectives. In 2009, Taiwan Supreme Court approved the admissibility of witness testimony which taken by foreign court and delivered some legal principles regarding mutual legal assistance. Upon these legal issues of this case, this paper will introduce some Japanese and European scholars theories, analyze similar Supreme Court cases regarding Cross-strait Joint Fight against Crime and Mutual Legal Assistance Agreement and the Taiwan-US Mutual Legal Assistance Agreement in Criminal Matters and raise some key points that will be of interest of legal practitioners. Therefore, expecting the research of this issue will be a ground stone for further study.