Objective To explore the possible mechanism of Heijiang Dan（ 黑绛丹） treating radiodermatitis.Methods Fifty-five rats were established Ⅳ-grade radiodermatitis animal models by60 Co source local irradiation.Forty-eight successfully modeled rats were randomized into Heijiang Dan group

control group 1

control group 2 and model group

12 rats in each. The groups were externally applied Heijiang Dan solution

recombinant human epidermal growth factor topical solution

water soluble vitamin E and normal saline 1 ml respectively

once every day for 10 days. Besides

the blank group was established with 12 rats

which was externally applied normal saline at the same location as the model group rats. Ultrastructure of wound tissue cells in all groups were examined by transmission electron microscope. The protein expressions of wound tissue cell apoptosis related factors in all groups were detected

including death related factor（ Fas）

death associated factor ligand（ Fas L）

cysteine-aspartate protease 3（ Caspase-3）

cysteine-aspartate protease 8（ Caspase-8）

cysteine-aspartate protease 9（ Caspase-9）

B cell lymphoma 2（ Bcl-2）

B cell lymphoma 2 related X protein（ Bax）

antioncogene p53（ p53）

cytochrome C（ Cyto-C） and apoptosis inducing factor（ AIF）. Results In the model group

nuclear chromatin concentrated

with swelling mitochondrial and rough endoplasmic reticulum expansion

which showed apoptotic cell change. In the Heijiang Dan group and the control 1 group

the structure of cell mitochondria was normal

with collagenous fiber and rich in desmosomes. In the control 2 group

nuclear chromatin concentrated

with rough endoplasmic reticulum expansion. Compared with the model group

the expressions of wound tissue Fas

Bax

Caspase-3

Caspase-8

Caspase-9

Cyto-C and AIF in the Heijiang Dan group decreased

while Bcl-2 expression increased（ P < 0. 01）. Compared with the control 1 group

the expressions of Fas

Caspase-8

p53

Caspase-3

Bcl-2

Cyto-C and Bax in the Heijiang Dan group increased（ P <0. 05 or P < 0. 01）. Compared with the control 2 group

the expressions of Caspase-8

Bax

Caspase-9

Cyto-C and AIF in the Heijiang Dan group decreased

while Bcl-2 and Fas L expressions increased（ P < 0. 05 or P < 0. 01）.Conclusion Heijiang Dan might reduce the extent of rat radiodermatitis damage by inhibiting local wound tissue apoptosis and regulating the expressions of apoptosis related protein.