Abstract: The isomerization of gibberellin A3 (GA3) to iso-GA3 in aqueous solutions results in losing biological activity of GA3. The inclusion compound of GA3 with hydroxypropyl-β-cyclodextrin (HP-β-CD) was prepared in order to enhance the stability and activity of GA3 in aqueous solution. The formation of inclusion compound was detected by the UV spectroscopy. The optimal condition was established by the orthogonal test. The best results was obtained using the mixture of HP-β-CD and GA3 (1:1 mole ratio) stirring for 2 h at 35 ℃ in a diethanolamine solution which contained 20% Tween-80 as the emulsifier. The inclusion rate was 81.7% under the optimal condition. Moreover, the stability of the GA3-HP-β-CD inclusion complex was evaluated by the biological test on elongation of pea's stem. The active component of GA3 in an aqueous solution was quantitated using ultra performance liquid chromatography (UPLC). Nearly all GA3 molecules were degraded and lost the biological activity after 14 d at 54 ℃±2 ℃. Whereas, the degradation ratio of inclusion compound was only 34% under the same condition. This study showed that the inclusion compound of GA3 with HP-β-CD might be an effective way to raise GA3 stability in aqueous solution.