Abstract: Under the condition of relative humidity less than the critical relative humidity,the discoloration rate and decomposition rate of vitamin C tablet and the discoloration rate of vitamin Ctablet in solution were studied at temperatures 60～90°C and relative humidities 60%～80%. Thegeneral equation of the relationship between the apparent rate constant k, absolute temperature T andrelative humidity RH is: k=k′exp(-E/RT) exp(mRH) ,where k′and m are constants,E is apparentactivation energy. The values of k′, m and E for discoloration, decomposition and discoloration insolution are different.