Abstract: AIM: To study the effect of light and heat on the stability of rotundine sulfate injection. METHODS: Accelerated tests upon exposure to light at high temperatures were employed. RESULTS: The degradation of rotundine sulfate injection in isothermal heating experiments and the exposure experiments to light at high temperatures obeys zero order kinetics. The total degradation rate constant k caused by both light and heat can be divided into two parts: k=k_dark+k_light , where k_dark andk_light are the degradation rate constant caused by heat and light, respectively. The k_light can be expressed as k_light=A_light·exp(-E_a,light/RT)·E, where E is the illuminance of light; A_light an experimental constant related to the light source; E_a,light an experimental constant independent of light sources. CONCLUSION: Since the form of k_light is similar to the Arrhenius equation, it is suggested that E_a,light might be the observed activation energy of the subsequent processes of the photochemical reaction. This viewpoint can be supported by the fact that the E_a,light is independent of light sources. Based on the effect of both light and heat on the degradation, the shelf life of rotundine sulfate injection under indoor daylight at room temperature was predicted, and the result was comparable to that determined by a long-term storage test.