Abstract: Sulforaphane (SFN) is an organosulfur compound found in brassica vegetables. The present study was undertaken to investigate the defending role of sulforaphane at a dose of 9 μmoles/mouse/day against the cellular dysfunction in benzo(a)pyrene [B(a)P] (100 mg kg^-1 b.w., i.p.) induced experimental lung carcinogenesis. The sub cellular derangements were assessed by the cytotoxic and cellular functional markers, lysosomal enzyme leakage and enzymes of nucleic acid metabolism. The concept of free radicals contributing to carcinogenesis was confirmed by evaluating thioredoxin reductase and heme oxygenase. The carcinogenic biomarkers were complemented by immunohistochemical analysis of cell proliferating nuclear antigen-Ki67 and measurement of serum carcinoembryonic antigen by ELISA. Our work proves the chemoprotective potential of sulforaphane in vivo against cellular derangements caused by B(a)P in the process of carcinogenesis.