Abstract Objectives To investigate the effect of adiposity status, salivary physicochemical parameters, and inflammatory biomarkers on the salivary abundance of the two main cariogenic bacteria Streptococcus mutans and Streptococcus sobrinus among Hong Kong adolescents. Subjects and Methods This study included 180 adolescents aged 12–15 years from Hong Kong local secondary schools. Anthropometric measurements and oral health examinations were performed. Saliva samples were collected to measure salivary physicochemical parameters, protein biomarker levels, and salivary abundance of Streptococcus mutans , Streptococcus sobrinus , and total bacteria. Results Adolescents with general overweight/obesity or central obesity had significantly higher salivary Streptococcus mutans abundance and total bacterial load, lower stimulated salivary flow rate, and lower secretory phospholipase A 2 group IIA levels than the lean controls. Adolescents with general overweight/obesity (OR = 3.33; 95% CI: 1.28–8.65) and those with central obesity (OR = 2.47; 95% CI: 1.02–6.00) had a significantly higher chance of having high salivary abundance of Streptococcus mutans than the lean controls after adjusting for confounders, with a similar detection rate of salivary Streptococcus sobrinus . Conclusion General overweight or obesity and central obesity were associated with a high salivary abundance of Streptococcus mutans but had no significant effect on salivary Streptococcus sobrinus .