© 2018, The Society of The Nippon Dental University. We investigated the relationship between the number of pairs of posterior teeth and metabolic syndrome (MetS), abdominal obesity (AO), and obesity, among Japanese adults. In 2005, 2,807 Japanese adults aged 25–74 years participated in the Survey of Dental Diseases and the National Health and Nutrition Survey. Based on the survey data, BMI, AO (JAS) determined by the Japan Atherosclerosis Society, AO (IDF) by the International Diabetes Federation, and MetS were assessed. Total functional tooth units (t-FTUs) were scored with pairs of opposing posterior teeth, including artificial teeth. Subjects were divided into three categories of chewing ability based on the score of t-FTUs: Poor (if score ≤ 9), Good (if score = 10–11), and Complete (if score = 12). The relationships between chewing ability and BMI ≥ 25, BMI ≥ 30, AO (JAS), AO (IDF), and MetS were tested using univariate and multivariate logistic regression analysis. The chewing ability was significantly associated with MetS, AO, and obesity in the univariate and multivariate logistic regression analysis. Adjusted OR of “Poor” compared to “Complete” were 1.51 (95% confidence interval (CI), 1.24–1.84) for BMI ≥ 25, 2.10 (95% CI 1.40–3.14) for BMI ≥ 30, 1.31 (95% CI 1.07–1.61) for AO (JAS), 1.40 (95% CI 1.15–1.70) for AO (IDF), and 1.34 (95% CI 1.04–1.72) for MetS. All were statistically significant. Preventing tooth loss and maintaining pairs of good chewing ability may be important factors in preventing MetS, AO, and obesity.