Aim To study, whether the consumption of regular tea/coffee (methylxanthines) increases the risk of oral cancer in patients with smoking and smokeless tobacco habits. Materials and methods This study was conducted on a total of 90 oral cancer and precancerous patients, from western Maharashtra (India) males in the age group of 20 to 45 years who were with smoking and smokeless tobacco habits; also regular tea/coffee consumers were subjected to biochemical parameters such as aspartate transaminase (AST) and alanine transaminase (ALT) from saliva and serum of patients with oral precancer (submucous fibrosis, leukoplakia) and oral cancer patients and compared with 90-age and sex-matched controls. Individuals consent was taken to measure their biochemical parameters, by using Hafkenscheid method in whole saliva and serum. Statistical analysis of variance (ANOVA) with Tukey's correction for multiple group comparisons was performed using Student t-test. Results Results show, that a statistically significant increase in value (p < 0.05) in ALT, AST in both saliva and serum was observed in precancerous and oral cancer patients among the study group as compared to the control group. Conclusion In the present study, there was increase in the levels of ALT, AST enzymes in both saliva and serum levels in the study group as compared to the control group which was statistically significant (p < 0.05) suggesting that long-term exposure of methylxanthines results in impairment of salivary gland antioxidant system which may affect the anticarcinogenic action of saliva. Clinical significance Oral fluids may be utilized effectively to study the variations in the biochemical constituents of saliva of leukoplakia, submucous fibrosis and oral cancer patients. How to cite this article Zubairy YF, Patil VW, Benjamin T, Jangam D, Bijle MNA, Patil S. Effect of Methylxanthines (Coffee/ tea Consumers) on Oral Precancer and Oral Cancer Patients with Smoking and Smokless Tobacco Habits. J Contemp Dent Pract 2012;13(6):745-748.