This article explores the issue of admissibility of evidence obtained through mutual criminal assistance between mainland China and Hong Kong. First, confessions obtained by hope of advantage are inadmissible in Hong Kong courts. However, evidence derived in such a manner cannot be used as grounds by the mainland court to exclude evidence. Second, if the police officer fails to give proper caution before questioning the suspect in Hong Kong, then this could render the following statement inadmissible. In contrast, the suspect will not be cautioned to his right to silence before interrogation in mainland China. Third, the court judge in Hong Kong tends to use a composite hybrid approach to exclude evidence obtained from entrapment. However, the rules of mainland do not allow for the use of entrapment as legal grounds to suppress evidence. The above comparisons show that relevant requirements should be incorporated into letters of request for taking of evidence through legal assistance.