Objective: Despite its sensitivity to light, atenolol has been manufactured as a film-coated tablet with normal blister packaging by several pharmaceutical companies in Bangladesh. The aim of this study was to investigate the extent of light-induced potency degradation of a randomly selected film coated brand of atenolol.Methods: Atenolol tablets were exposed to different lighting conditions such as normal room light, direct sunlight and different incandescent lights (25W and 40W). Subsequently, UV spectroscopy technique was employed to determine the relative reduction of light absorbance compared to their respective controls. Thereafter, photolytic degradation was calculated by means of the potency reduction of tablets.Results: In all lighting conditions, atenolol tablets underwent exposure dependent gradual decrease in potency. Except for normal room light condition, a significant decrease in potency was found even after 4 to 6 h of exposure to all lighting conditions. After 6 h, potency reduction was found at 40-47%, 26-38% and 34-36% in the samples exposed to direct sunlight, 25 W bulb, and 40 W bulb respectively. Although the shelf life of the film coated tables was 2 y, surprisingly, statistically significant reduction in potency was observed within only 30 d in room light condition.Conclusion: In order to protect from light, blister packaging is not sufficient for film coated atenolol tablets. Photo-stability of all brands of atenolol must be ensured either by protective packaging materials or by optimizing the formulations.