Background: P300 represents the long latency auditory event related potentials that serve as an objective measure of information and cognitive processing. Smoking remains a serious global threat, yet a modifiable risk factor that may influence cognitive functioning. While the adverse effects of smoking are well appreciated, effect of smoking on the cognitive marker P300 has received less attention. Objectives: To assess the effect of smoking on auditory P300 event related potential. Materials and Methods: 60 male individuals in the age group of 40-60 years were recruited for the present study. 30 were smokers and 30 were non-smokers. The latency and amplitude of P300 event related potential was recorded at Cz and Pz and compared between smokers and non-smokers. p< 0.05 was considered statistically significant. Results: There was a significant increase in latency of P300 at both Cz and Pz in smokers compared to the non-smokers. There was a significant decrease in the amplitude of P300 at both Cz and Pz in smokers compared to the non-smokers. Conclusion: These results suggest that smoking causes significant alteration in auditory P300, suggesting impaired cognitive processing. Hence intervention may be suggested at earlier stages to smokers to maintain good cognition.