Abstract: This study sought to answer the question of what are the causes of marital infidelity in the Iranian family. To Answer the Research Question, Qualitative Meta-Synthesis (QMS) Method Were Used. Then, 78 Scientific Papers Which Were Considered Marital Infidelity in Iran were identified and were Analyzed. The results showed that the FACTORS of infidelity in Iran can be classified into 9 main categories, including: 1. Social FACTORS, 2. Psychological FACTORS, 3. Cultural FACTORS, 4. Family FACTORS, 5. Personal FACTORS, 6. Relational FACTORS, 7. Economic FACTORS, 8. Media FACTORS, 9. Contextual FACTORS. Each of the main Categories is divided into Different Subcategories. The Social FACTORS of infidelity were including “Infidelity Opportunities”, “Friend groups” and “Environmental Conditions”. Psychological FACTORS of Infidelity Were Including “Personality Type”, “Attachment Styles”, and their “Love Schema”. Cultural FACTORS have Pointed to “Change in Beliefs and values” and “the level of Religious Education” of people. The Family FACTORS were including “Inappropriate Marriage”, “Family Conflict” and “the Kind of Family Background of people”. The Personal FACTORS are “Sexual Dissatisfaction”, “Emotional Dissatisfaction”, “the Feeling of Loneliness”, “the Spouse Unavailability”, “Weakness in Controlling Spouse”, “Domestic Violence”, “Revenge of the Spouse” and “the Role of the Third Person in the Relationship”. The Economic FACTORS are including “the Economic Status of the person”, “the Role of Economic Problems”, “the motivation of entering into infidelity under the Pretext of JOB promotion”. The media FACTORS Were Emphasized on “weakening Iranian Values through Social Media Networks and Foreign Satellite Channels” and “Producing of New Needs by Media”. Finally, the Contextual FACTORS were including the Role of “Age” and “Gender” in the Infidelity. Findings showed that Infidelity Occurred in the group of men and youth in Iran, more than other Social Groups.