OBJECTIVE To observe the effect of Guizhi plus Gegen Decoction (GGD) on ultrastructural changes of intervertebral disc annulus fibrosus cells. METHODS Rats' intervertebral disc annulus fibrosus cells were isolated and cultured using adherence wall screening method. After annulus fibrosus cells were intervened by GGD, the microstructure and ultrastructural features of untreated annulus fibrosus cells and annulus fibrosus cells treated by GGD containing serum at different concentrations were observed under optical microscope and electron microscope. RESULTS Under optical microscope, most annulus fibrosus cells showed irregular polygons and few in star shape with rich superficial ecphyma. The nuclei were oval, large and complete. Under electron microscope, most cells in the blank group were oval after intervened by GGD containing serum at different concentrations. The nucleus was large, deviated, and irregular, the heterochromatin scattered diffusely, partial mitochondria vacuolized, and rough endoplasmic reticulum dilated. In the low dose GGD group, increased mitochondria and condensed density could be seen. The rough endoplasmic reticulum were expanded, lipid drops or glycogen could be occasionally seen. In the middle dose GGD group, increased endoplasmic reticulum expansion and condensed density could be seen. More medium density protein sediment could be seen. Increased mitochondria with condensed density could be seen, showing irregular cystic form with various sizes nucleus. In the high dose GGD group, increased rough endoplasmic reticulum with obvious expansion could be seen. More high density protein sediment could be seen. The nuclei were deviated. More mitochondria could be seen with secretory granules in them. CONCLUSIONS After intervened by GGD containing serum at different concentrations, the ultrastructure of annulus fibrosus cells were manifested as follows: (1) The endoplasmic reticulum increased more in the middle and high dose GGD groups than in the blank group and the low dose GGD group. Greater density protein sediment occurred, especially in the high dose GGD group. (2) GGD played an important role in preventing ultrastructural changes induced by the degeneration of annulus fibrosus cells.