Objective: Married life like other matters and phenomenon has its own special damages and problems too that one of this main damages of married life is sexual unlawful relation ship. Among this, the subject that draws researchers' attention is what factors cause the tendency of married men and women to unlawful sexual relationship? Method: This research is kind of measurmental or planning studying that the researcher pays in it to sociology and psychology features about what people think and do about unlawful relation ship and the relation ship between mental and social changeables. Finding & Result: Finding represents this subject that the factors of sexual unsatis faction in married relation ship, feeling of revenge about unfaithful ness of wife and in like of various are effective in tendency of married men and women to sexual unlawful relation ship. The results in this research showed that the tendency of unlawful relation ship between men is more than women and it is the main factor in their tendency to unlawful relation ship, motivation of sexual tensions, unsatisfaction of moral relation ship inability in solving married encroachment.