Abstract: Objective To detect saliva mutans streotococci and plaque indexes between caries-active and caries-free undergraduate students by Dentocult SM,and to assess whether they can serve as indicators of risk factors for caries high risk persons. Methods Plaque index was detected among 48 18~25 years old undergraduate students, which were divided into caries-active group and caries-free group, with 24 students in each group. Dentocult SM was adopted to detect the saliva streptococcus mutans among randomly selected 23 subjects from caries-active group and 16 subjects from caries-free group. Results The plaque index of caries-active group and caries-free group was separately 3.65 ± 0.64 and 3.42 ± 0.65, with no statistical significance in the difference between the two groups(p=0.239),while there was statistically significant difference in saliva mutans streptococci between two groups (p=0.003).Conclusion Saliva mutans streptococci can be considered as an indicator to assess caries high risk persons by Dentocult SM.