Oral cancer is the fifth leading cause of cancer death in Taiwan, and the prevalence of metabolic syndrome (MS) has also increased globally. The purpose of this study was to investigate the correlations between the components of MS and oxidative stress and inflammation in patients with oral cancer based on their areca-nut-chewing habits. Two hundred patients diagnosed with oral cancer were recruited, and metabolic parameters, oxidative stress, antioxidant enzyme activities, and inflammatory markers were measured. 63% of the subjects have concomitant MS. Subjects who had an areca-nut-chewing habit had significantly higher levels of fasting glucose (p = 0.04), oxidative stress (p = 0.02), and inflammatory markers (p = 0.02) than those who never chewed. High-density lipoprotein-cholesterol level (p = 0.03) and superoxidase dismutase activity (p = 0.02) were significantly lower in individuals who had chewed or were currently chewers. Areca-nut-chewing habit was associated with the increased risks for MS and hypertriglyceridemia; the components of MS were positively correlated with oxidative stress and inflammation. In conclusion, patients with oral cancer who had an areca-nut-chewing habit exhibited higher levels of oxidative stress and inflammation, which might be related to an increased risk of MS.