The aim of this study is to investigate the correlation between the control of diabetes and the number of cariogenic bacteria in patients with diabetes and thereby reveal the influence of diabetes on the incidence of caries. we compared oral microbial flora in patients with different levels of HbA1C (glycated haemoglobin). Cariogenic bacteria were identified according to Dentocult System, When comparing patients with different levels of glycaemia control, the detected number of cariogenic bacteria in the patients with poor control of diabetes was significantly higher than in those with good glycaemia control. The findings suggest that patients with poor control of diabetes tend to have a higher risk of dental caries than the patients with good control of diabetes.