Abstract: The vagina is a dynamic and finely tuned ecosystem in which homeostasis depends on mutually beneficial interactions between a human female and her resident microorganisms. In recent years，the development and introduction of cultivation-independent molecular-based techniques have provided new information about the composition of normal vaginal flora，“normal flora” is a concept currently being redefined.Dominance by lactic-acid producing microbes appears to be the cornerstone of microbial health. Numerous factors（both internal and external） have the potential to disrupt the vaginal ecosystem's fragile balance，and different racial groups，different geographical region have significant difference in what is the dominant vaginal organisms.

Key words: Vagina, Lactobacillus, Age factors, Anti-bacterial agents, Contraception