Objective: To study the relationship between genetic diversity within P-region and V-region and C-terminus of surface protein of Streptococcus mutans isolates and adherent abilities. Methods: The clinical isolates of S. mutans (serotype c) included two groups with different adherent abilities, which were derived from previous work in our experimental lab. The genome DNA was extracted, and spaP-pv (2060-3157bp) and spaP-c (4003-4851bp) were amplified by PCR respectively. Genetic diversity was assessed by restriction fragment-length polymorphism (RFLP) with restriction endonuclease AluI. Sequence analysis of spaP-pv in 19 strains was performed. Results: 1. Two different genotypes (a, b) of spaP-pv were revealed and the distribution of two genotypes in strains with different adherent abilities had statistical significance (p < 0.05). Sequence analysis of spaP-pv identified two different DNA fragments between a, b genotype strains and they were located in V-region of surface protein. 2. Two genotypes of spaP-c were revealed when digested with AluI. The distribution of genotypes in strains with different adherent abilities was not different. Conclusion: It suggests variation of gene encoding V-region may account for different adherent abilities of surface protein of S. mutans isolates.