The principle of dual criminality narrows the use of mutual legal assistance in criminal matters when it is applied without any flexibility. As a result, there is a trend to apply the principle more loosely or to refrain from the application of the principle altogether in the international conventions, treaties, mutual legal assistance agreements and domestic laws in recent years so as to coordinate the relation between the application of the principle and the encouragement of the broader use of mutual legal assistance. With regard to the mutual legal assistance in criminal matters in practice, in order to loosening up the application of the dual criminality principle, different methods including excluding the application of the principle or to substitute with the abstract dual criminality principle to narrow the application of the principle of dual criminality, ruling out the application of the principle in whole or in part by the requested country are adopted in the international conventions, treaties, mutual legal assistance agreements and domestic laws. However, how to loosely apply or cease the application of the principle is quite diversified with regard to the implementation of mutual legal assistance in criminal matters. Is the regulation of the principle of dual criminality in the relevant laws, treaties, mutual legal assistance agreements and the Money Laundering Control Act in Taiwan in conformity with the regulation of international conventions including the FATF 40 Recommendations? It is worthwhile to categorize and analyze the regulation thereof so as to provide as reference for future application and amendment.