||Protein pharmaceuticals are in mass production due to the advances in the hybridoma and genetics engineering but its stability remains an issue. 2 ~ 10 °C should be maintained during the transportation and production to achieve stability, but this is expensive and not always available. Freeze drying is a potential alternative but its effect is unknown. The instability of horseradish peroxidase (HRP), a representative enzyme, in aqueous solution at 2 ~ 40 °C was investigated. The kinetics of the catalytic activity reduction was first order and the rate constants were calculated. Arrhenius activation energy is 61.52 kJ/mol. Then the instability of freeze dried powder HRP stored at 4 ~ 40 °C, under nitrogen protection or exposed to air were examined. The activity change is not temperature dependent but experienced a drop and then an increase as a function of time. The activity change of the HRP exposed to air and Fourier transform infrared spectra (FTIR) results indicated that the activity change was a result of oxidation. The enzyme can survive in an ambient temperature for more than one month under nitrogen protection but not I air. Finally, immunoglobulin G (IgG) which has a potential for human disease treatment was freeze dried with different formulations. The bioactivity of IgG was best preserved with hepes buffer saline and a mass ratio of IgG to trehloase (a disaccharide) at 1:1. FTIR showed that unfolding and conformational change can be effectively reduced by adding protectant. In summary, kinetics method can be applied to the protein instability analysis; freeze drying with the addition of protectant can preserve the protein.