Background This study explores the association between chronic periodontitis and renal dysfunction in type 2 diabetic mellitus (T2DM) patients. Methods An observational study was conducted in 169 T2DM patients with chronic periodontitis. Patients were divided into 2 groups according to presence of normal renal function (n=111) and renal dysfunction (n=58), and oral health behavior-related variables were obtained by questionnaire. Periodontal status was examined, and pocket probing depth (PD), clinical attachment level (CAL), and bleeding index (BI) were measured. Results The severe periodontitis group had a significant higher HbA1c level (8.53 1.61%) as compared with the mild and moderate periodontitis groups (7.68 +/- 1.58%) and (7.35 +/- 1.45%), P=0.001. Compared with patients with normal renal function, patients with renal dysfunction had a higher PD value, higher CAL value, fewer remaining teeth, and were less likely to have remaining teeth >= 20. The percentage of sites with PD >= 4mm (52.8% vs. 41.67%) was significantly greater in patients with renal dysfunction. There was no difference in the scores of oral health knowledge assessment between the 2 groups. After adjustment by gender, age, BMI, smoking, hypertension, and HbA1c, the percentage of the sites with PD >= 4mm was an independent risk factor of renal dysfunction in T2DM patients. Conclusion In patients with T2DM, those with periodontitis may be more susceptible to decreased kidney function.