The study departs from complexity of society as a general inclination in modern social life. Technological progress likes in USA and Europe such as transportations and communications will often appear many problems in inter ethnic interaction, culture, and religion. The condition is as same as Indonesia with its complexity of society and kind of back ground such as ethnic, religion, race (SARA), and culture. Social interaction among people and their complexity could make problem of SARA and it's not unusual supporting among parties to power their ethnic identity and primordialism. How ever, it doesn?t mean to weaker opinion that intensive of contacts as a result of social interaction would disappear differences among parties in social life.It's good enough, one effective way of national assimilation through inter ethnic or population marriage. Marriage function is family legalization, and among other things goal to reproduce and for the next will be make a social reproduction. The social reproduction performances like as "new man". The new man's identity is fully depending on one parties domination of parents and social milieu, like as residence, job - places, educations, and customs. And accordingly with above, the study will observe marriages between Dayak people with Chinese womb in District of Samalantan, Regention of Sambas, West Kalimantan.To express the study result, there are three main aspects will be studied, i.e. social adaptation, individual adjustment, and socialization.Main theory base on the study is assimilation theory of Milton M. Gordon (1964) expressed three central inclinations, i.e., "Anglo-conformity", "melting-potn, and "cultural-pluralism". Other theory according to the study is from Zanden (1970), Goode (1985), Firth (1954), Barth (1970), Johnson (1981), Horton and Hunt (1984), Herskovits (1958), Haviland (1985), Linton (1945), Mennel (1974), and Merton {1975).The study support to understand more about inter ethnic marriage function as an effective way in national assimilation. The result hopes could be used to developed knowledge?s in sociology and anthropology, and even for in-creased context in political and economic science. More over, the result could be used by government or other party who has right "to arrange" assimilation policies.The data collecting method are taken from questionnaire using, observation, and interviews. As data resources and information, samples determined with total 100 respondents {50 marriage pairs) and key informant with total ten persons. Sample choosing method is done purposely and in﷓formant too. Analysis to be used is qualitative with using interpretation technique on data classification/information.From a couple of dates and information have been taken from methodological procedure to be determined with prepositional way such as question likes above, and based on relevance theories, consequently the study result ex-pressed as follows:Marriage between Days-Chinese wombs appears a symbiotic relation between both or parties in economy. The marriage bears political opportunity to Chinese caused of the Chinese would be protected by Days as original in habitants. Besides, the kind or marriage is a mediator between both of parties, family, and society.Although there are many difficulties experienced by both of the parties to keep going their marriage, the family who is legalized by the marriage would be an effective way in national assimilation, and at least it could be as socialization way of their children as "new man".As a reason, there is unreal 100 percent assimilation is happened. It's same with marriage they. The marriage could be stopped and may be followed on. It is so depending upon ethics and condition one of parties. And so the individual and society milieu.But as same as the marriage have noble goal, e.g. developing their womb and preparing family and good society, so the Dayak-Chinese marriage has a glorious goal, e.g. getting good citizen based on under standing each other between the parties include society.