Sexual Relationship is an essential human-basic need which intervens social structure and fertility among groups of people in their society. The process of sexual relation is intiated in the puberty period. However, consequence of sexual relation with inappropriate age will create critical problems for teenages themselves, their families, and society, especially among those female teenagers with low socioeconomic status will face undesired problems. According to those mentioned, the main objective of this study was to determine sexual relation behaviors, and factors affecting sexual practices among female workers in factories in Bangkok and neighboring provinces. Multistages Random Sampling Technique was performed to select 503 female workers with age of 15 - 20 years from various factories in Bangkok, Samutsakorn and Pratumtani Provinces, of which 230 were from Bangkok and 273 were from two provinces. A self Administered with structured form of questionnaire was used for data collection. This form consists of parts dealing with the determination of knowledge, attitude. and practice in sexual relation. traditional obedience to parents concerning sexual relations, previous learning experiences from various sources. Data analysis techniques employed include Pearson product moment correlation, one way, two-way three-way and multi-way analysis of variances, and the multiple regression techniques. The findings showed that sexual behavior significantly relate to individual characteristics, knowledge and attitude toward {sexual relation, and learning experiences concerning sexual relation from various sources and direct experiences. Sexual behavior was determined by the previous sexual experiences, income, attitude toward sexual relations, and knowledge about sexual relations respectively. The differences of knowledge, attitude, obedience to parents, and previous learning experiences affect difference in actual sex behavior among those female workers. The findings imply some suggestions that both governmental and non-governmental organizations should take into the consideration to formulate policy and plan for sexual behavior improvement among teenage female workers through informal education, and other effective education program networks, including counseling with emphasis on family life education. The importance of family as a social institution should be emphasized so that positive attitude toward sexual relation and value will be formed among those workers which consequently influence their desirable sexual behaviors. Finally, the desirable fertility in terms of quantity and quality will be achieved in the future.