Aim of the study: Oral squamous cell carcinoma (OSCC) is most commonly develops from pre–existing potential/precursor malignant (PM) lesions. Earliest identification of potential/precursor malignant lesion can save many live by being affected by oral cancer. Therefore the techniques for early diagnosis have been considered as useful method in practice. Toluidine blue (TB) application is commonly used as an adjunctive aid for oral premalignant and malignant lesions. The aim of this study was to evaluate the reliability of Toluidine blue in the detection of potential/precursor malignant and malignant lesions. Methods: In this cross–sectional study clinically diagnosed 25 patients of potential/precursor malignant lesions and 25 patients of oral squamous cell carcinoma were selected from OPD. After taking written consent Toluidine blue application was done for all the patients, scalpel biopsy was taken for all of them. Clinico–pathological comparison was done and results were analyzed by chi–square test, assessed for sensitivity, specificity, Positive Predicative Value (PPV) and Negative Predictive Value (NPV). Results: Potentially malignant and malignant lesions showed different sensitivity and specificity reaction with difference in positive and negative predictive values. However there was statistical significant difference among PM lesions and OSCC. Conclusion: Toluidine blue staining has more sensitivity hence with highest PPV for malignant lesions, however it was almost equal sensitive and specific for PM lesions. Toluidine blue staining in OSCC and PM lesions is definitely helpful in many ways, but results should be carefully interpreted and one should not solely rely on it.