Background: Deregulation of β-catenin is associated with malignant transformation; however, its relationship with potentially malignant and malignant oral processes is not fully understood. The aim of this study was to determine and compare the nuclear β-catenin expression in oral dysplasia and oral squamous cell carcinoma (OSCC). Material and Methods: Cross sectional study. Immunodetection of β-catenin was performed on 72 samples, with the following distribution: 21 mild dysplasia, 12 moderate dysplasia, severe dysplasia 3, 36 OSCC including 19 well differentiated, 15 moderately differentiated and 2 poorly differentiated. Through microscopic observation the number of positive cells per 1000 epithelial cells was counted. For the statistical analysis, the Kruskal Wallis test was used. Results: Nuclear expression of β-catenin was observed in all samples with severe and moderate dysplasia, with a median of 267.5, in comparison to mild dysplasia whose median was 103.75. Only 10 samples (27.7%) with OSCC showed nuclear expression, with statistically significant differences between groups ( p < 0.05). Conclusions: Our results are consistent with most of the reports which show increased presence of β-catenin in severe and moderate dysplasia compared to mild dysplasia; however the expression of nuclear β-catenin decreased after starting the invasive neoplastic process. This suggests a role for this protein in the progression of dysplasia and early malignant transformation to OSCC. Immunodetection of β-catenin could be a possible immune marker in the detection of oral dysplasia