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Introduction: Conventional chest CT is usually performed in the setting between 220-280 mAs. Increase use of CT in recent times has the potential to increase radiation burden to the general population. The purpose of this study was to evaluate the image quality in CT Chest with 50% mAs reduction. Methods: This prospective study was done in 101 patients with age above 18 years and BMI less than 25kg/m2 who were referred for CECT chest examination. A 16 slice multi detector CT scanner was used to acquire non contrast at 120 kVp and 140 mAs, a modified protocol with 50% reduction in mAsand contrast enhanced scan at standard protocol of 120 kVp and 280 mAs. The images of plain and contrast enhanced scans were evaluated by two expert radiologists and given the image quality score in 5 point scale (1-worst, 2-suboptimal, 3-adequate, 4-good, 5-excellent) to each. Image noise was measured in images of each patient. Patient weight, height and BMI were recorded and correlated with image quality score. Statistical analysis was done with relevant test. Results: The overall image quality with standard protocol was significantly better (p<0.05) than modified protocol. The modified protocol had acceptable image quality score for patients with weight< 60 kg, BMI<25kg/m2. The CTDIvol was 11.15 with reduced mAs and 22.15 with standard mAs resulting in significant reduction in radiation dose of about 49%. Conclusion: Image quality of modified protocol with 50% mAs reduction i.e.140 mAs is acceptable for average built patients and not patients with large anthropometric parameters. [ABSTRACT FROM AUTHOR]