Although there are various risk factors in the literature, the established primary risk factor for oral cancer is tobacco and betal-nut chewing habits. It is believed that pathogenesis of oral cancer depends on the aetiology. To assess the histopathological grade and Ki-67 expression in tobacco (smoking/smokeless) and non-tobacco (betal nut/pan masala) habitual buccal mucosa cancer. The cross-sectional study was carried out in Regional cancer centre, Tamilnadu. Proliferative marker, Ki-67 expression was determined by immunohistochemistry using biotin-streptavidin method. The study includes 117 buccal mucosa cancer patients (61 male and 56 female). According to WHO grading system, high frequency observed with well differentiated squamous cell carcinoma 48 (41%) followed by moderate 46 (39.3%) and poorly differentiated 23 (19.7%). The cut-off value 50% was used to categorize Ki-67 expression into low and high labelling index (LI); 96 (82%) buccal mucosa cancer and 4 (3.4%) adjacent normal mucosa patients showed high Ki-67 expression. The present study showed highly significant association of histopathological tumor grade and Ki-67 expression by Chi square and paired test  < 0.05. All the patients were grouped as tobacco 87 (74.4%) and non-tobacco habitual 30 (25.6%) in 3:1, respectively. Further, the risk habits identified with significant differences of tumor grade ( = 0.028) and Ki-67 at  < 0.05. Thus, the study revealed that the nature of cell differentiation and proliferation was strongly related to consumption of carcinogen in both tobacco and non-tobacco form. Therefore, histopathological grade and Ki-67 could be used as a reliable biomarker to understand the biological behaviour of risk habits which might helpful for further treatment therapeutics.