On the evidence for the impeachment, in literature, four problems are in discussion. At first, whether a hearsay evidence is admissible for impeachment, although it is not admissible in view of the hearsay rule. Second, whether the oral evidence of the defendant in trial is impeachable, and whehter the defendant's pre-trial statements protocol of the police is admissible for impeaching the oral evidence of the defendant in trial. At last, whether the authentification is required for the admissiblity of the hearsay written statement for impeachment. For first problem, though a hearsay evidence is not admissible according to the hearsay rule, it is admissible for impeachment. The hearsay rule is operated only where pre-trial statement is produced for asserting the truth of the statement. Because impeachment is not asserting the truth of the pre-trial statement, but swaying the crediblity of the oral evidence in trial, hearsay rule is not operated when the evidence is produced for impeachment. For second problem, the oral evidence of the defendant in trial can be impeached for the appropriate way of truth-finding. In practice, the prior inconsistent statement of the defendant can be often used for impeaching the oral evidence of the defendant in trial. § 312 ② of the Korean Criminal Procedure Act provides that the defendant's pre-trial statesments protocol is not admissible when the defendant or the counsel of the defendant denies the truth of the statesment. Because of the provision, some say that the defendant's pre-trial statesments protocol is not admissible for impeachment when the defendant or the counsel of the defendant denies the truth of the statesment. But the Court admits the defendant's pre-trial statesments protocol although the defendant or the counsel of the defendant denies the truth of the statesment, and it is with me on that. For the last problem, the majority in literature and the Court are with the opinion that the authentification is not required for the admissiblity of the hearsay written statement for impeachment. In this point I cannot agree with the Court. The requirement of the authentification is essential for producing all the evidences. It is a different rule from the hearsay rule. In my opinion, It could be said that the majority and the Court confuse the difference. It should be said that a hearsay written statement cannot be used for impeachment when it is not authentifcated.