Considering the important role of the family in the society and the mutual influence of the society and the family on each other, the strength and durability of the said institution is of great importance, therefore, after the conclusion of marriage, rights and duties are created for the couple and they have moral and legal responsibilities. The strength of the family institution depends on the adherence and loyalty of the couple, and lack of loyalty and betrayal is one of the challenges and damages that cause the disintegration and destruction of this sacred institution, therefore, considering the importance of loyalty and non-faithfulness and their decisive role in The strength and strengthening of the foundations of the family. The present study, which is a descriptive analysis method, was carried out with the aim of investigating the legal position of marital fidelity and infidelity from the perspective of Iranian and British law. Based on the results of the research, the implementation of the violation of marital fidelity in Iranian law is compared to British law. It is more detailed and wider, while in Iranian laws, civil and criminal enforcements are considered for violating the fidelity of spouses, and misbehavior and infidelity of the spouse can be documented in the divorce request of the wife, and the unfaithfulness of the wife also causes her to be deprived of paying alimony. In English law, in the beginning, unfaithfulness and infidelity of spouses had the guarantee of criminal and civil enforcement, and it could also