The effect of beta-carotene on the photostability of nisoldipine (NS) has been investigated. Light stability studies were carried out following the recommendations of the International Conference on Harmonization (ICH), version I, using a high-pressure mercury lamp, type HBO-50, equipped with the interference filter and Wood's filter to isolate 365 nm wavelength. The photodegradation process was assayed by means of UV spectrophotometry and the reversed phase High-Performance Liquid Chromatography (HPLC). The quantum yields of photodegradation of NS and NS in the presence of beta-carotene were determined using the Reinecke salt as a chemical actinometer. The methanol solutions of NS degraded following apparent first-order kinetics. The degradation rate constant decreased as beta-carotene concentration increased. To verify the photostabilising role of the dye, a Stern-Volmer plot was constructed. The results have proved that beta-carotene does not act as a photosensitiser.