In this study, I focused my arguments on what aspects the laws about the adultery and the divorce have been changed from the classical Roman law to the Christian period of the 4th-6th. First, I examined the Augustan law about the adultery, enacted about B. C. 18 and called often “Julian law for adultery repression.” The Julian law for adultery repression considered that the adultery was woman's sin. It offered to the husband and the married woman's father a right killing (ius occidendi) the adulterer without penalty. According to the Julian law, the husband had to divorce his wife before he accused her of adultery. If the adultery is proven, the adulterer and the adulteress were sentenced to a economic loss. In the period of Constantine, the fundamental notion of the Julian law and the Ius Occidendi were still unchanged. But the woman had to be divorced by his husband only after she was accused and proved guilty. And Constantine sentenced the death penalty to the adulterer and the adulteress, while Justinianus confined the latter in the monastery. As to the divorce, the Roman legal tradition sustained the marriage by marital affection (maritalis affectio) and the divorce by consent of two parties. But Constantine and Justinianus attempted to intervene a Roman custom of free divorce. Constantine promulgated a constitution limiting the unilateral divorce (repudium), but his law was made void twice and was vivified by Theodosius who lightened the conditions of the divorce and the penalty. On the other hand, Justinianus interdicted the bilateral divorce (divortium) but his law had to be recalled soon by Justine II, because it was contrary to the spirit of the Roman law about the marriage and the divorce by free consent.