Abstract: The dehiscent nut and incomplete hulls of thin-shelled walnut（Juglans regia）seriously influenced the quality of nuts and kernels. In order to explore the relationship between the development of nut shell and phytohormones，and to provide a theoretical basis for regulating the nut shell development. In this study，‘Zanmei’（thick-shell cultivar）and‘Liaohe 2’（thin-shell cultivar）walnut as material，the development of thin-shell and thick-shell nut shell was studied by Wiesner raction. IAA，GA，ZR and ABA contents were determined during the process of shell differentiation.‘Qingxiang’（moderate thickness shell cultivar）walnut as material，the characteristic，structure and components of mature nutshell were evaluated after treated by 6-BA，GA3 and paclobutrazol（PAC，a specific inhibitor of gibberellin biosynthesis）at different concentrations during shell development. The results showed that the shell development of‘Zanmei’and‘Liaohe 2’began at 45 days and 51 days after anthesis（DAF）respectively and the nut shell initially formed at 60 DAF，and then lignin within the shell deposited gradually. In pericarp，the GA，IAA and ZR content of decreased，and ABA content decreased firstly and then increased during the period of shell differentiation. 50 mg ? L-1 GA3 increased the thickness of the stone cell layer and fiber-cell layer，thickened the shell，enhanced suture force grade，and 100 mg ? L-1 PAC decreased the contents of lignin and polyphenol with the thinner of sclereid layer，sclerenchymatous cell layer and fiber-cell layer. 100 mg ? L-1 6-BA treatment decreased the longitudinal diameter，transverse diameter and side diameter of nuts significantly，but there was no change in the structure of the shell tissue. Conclusion：Shell development of‘Zanmei’was earlier than that of‘Liaohe 2’. For‘Qingxiang’，50 mg ? L-1 GA3 increased the thickness of sclereid layer，and 100 mg ? L-1 PAC inhibits the thickening of nut shell，indicating that GA is involved in the regulation of nut shell development. The nut became smaller after treated by 100 mg ? L-1 6-BA，but there was no change in the structure of shell tissue.

Key words: walnut, shell, phytohormone, lignin