Objective:To observe the effects of astaxanthin on paraquat poisoning-induced pulmonary fibrosis in SD rats, and explore the mechanism of pulmonary fibrosis. Methods:The rats were randomly divided into three groups, including the normal control group, the PQ model group, and the astaxanthin group. The PQ group and the astaxanthin group were intraperitoneal injected with PQ. In the next day, the rats were treated by intragastric administration once a day. The control group and the PQ group were treated by the same dosage of solvent. On day 7, day 14, day 28 after treatment, the rats in each group were sacrificed. The levels of hydroxyproline (HYP) and TGF-β1 were measured. The levels of matrix metalloproteinase (MMP) 1, MMP2, MMP9 and tissue inhibitor of matrix metalloproteinase1 (TIMP1) were determined in the serum of rat by ELISA, and the pathologic changes of lung tissues were observed by HE staining and Masson staining. Results:①HE staining and Masson staining results showed that the degree of fibrosis in the astaxanthin group was significantly lower than that of the PQ group. ②The hydroxyproline content of model group was significantly higher than that of the normal group (P<0.05). In the intervention of astaxanthin, the level of hydroxyproline in rat was decreased compared with the model group (P<0.05). ③TGF-β1 was expressed in the PQ model group. After intervention of astaxanthin, the expression of TGF-β1 was decreased, especially at day 28, and the difference was statistically significant (P<0.05). ④The expression levels of MMP1, MMP2 and MMP9 in the model group and the astaxanthin group were higher than those in the normal control group. The expressions of MMP1, MMP2, MMP9 after PQ poisoning were gradually increased, reached the highest point in day 14, then the expressions in day 14 began to decline but still higher than those of the control group. Compared with the model group, the contents of MMP9 and MMP2 in the astaxanthin group were decreased, and the difference was statistically significant (P<0.05) in the day 14 and day 28. TIMP1 had no significant difference between the model group and the control group during the intervention period (P>0.05). Conclusion:Astaxanthin can reduce the content of hydroxyproline, MMP9, and MMP2, inhibit the secretion of TGF-β1 in lung tissue, and decrease the collagen deposition in lung tissue of rats with pulmonary fibrosis, further reduce PQ-induced pulmonary fibrosis in rats.