Different social groups in the contemporary Iranian society are experiencing rapid transformation of values from traditional to modern, and from simple ways to complex and diverse ways when it comes to choosing a spouse. Therefore, from the point of view of sociologists, recognition of the new criteria and their comparison with the previous ones is of great importance. To this end, the present study was conducted to compare the criteria for finding a lifelong partner among different social groups in contemporary Iranian society. The method of this study is to conduct surveys, and its subjects consist of 15-65 year old urban and rural resident in the entirety of the country. The sample size is five thousand people selected by multistage cluster sampling. The descriptive results of the research show that among the criteria for marriage, personality traits (84. 29%), emotional-psychological characteristics (80. 22%) and religious beliefs (77. 81%) are considered as the most important criteria in Iran. The results obtained by testing the research hypotheses show that age, sex, marital status, education, socioeconomic status, ethnicity, method of approach, and religious attachment have significant relationship with criteria for choosing a partner, although the severity and weakness of these relationships are different among men and women. Therefore, these results indicate differences in the criteria for choosing a lifelong partner among different social groups in contemporary Iranian society.