Objective To investigate the effects and mechanisms of hydroxychloroquine sulfate (HCQ) on pulmonary fibrosis through the PI3K/AKt/mTOR signalling pathway. Methods Paraquat intraperitoneal injection was used to establish a mouse model of pulmonary fibrosis. Thirty-six SPF C57BL/6J female mice were randomly divided into a blank group, a paraquat group (20 mg/kg) and a HCQ intervention group. The HCQ intervention group was divided into two subgroups (10 mg/kg and 30 mg/kg) according to different doses. The general condition and body weight changes of mice were observed. twenty-one days later, lung tissues were stained with hematoxylin-eosin and Masson’s pathological staining, and the content of inflammatory factors (IL-1β, IL-6, TNF-α) and hydroxyproline (HYP) were detected by ELISA. Alpha-smooth muscle actin (α-SMA), E-cadherin (E-cad), the expression levels of PI3K/Akt/mTOR pathway-related proteins, phosphatidylinositol 3 kinase (PI3K) and protein kinase B (AKt), and mammalian target of rapamycin (mTOR) were detected by Western blot. The gene expression levels of α-SMA and E-cad were detected by q-PCR. Results Compared with the blank group, the mice in the paraquat group had lower body weight, worse general condition, higher serum levels of inflammatory factors, increased lung structure destruction and collagen deposition, significantly increased HYP content, and higher expression level of PI3K/AKt/mTOR signaling pathway related proteins (all P<0.05). The expression levels of E-cad protein and gene decreased, α-SMA protein and gene increased (all P<0.05). While the HCQ intervention group improved the degree of pulmonary fibrosis in different degrees, and the relevant indexes of PI3K/AKt/mTOR signaling pathway decreased compared with the paraquat group (all P<0.05). Conclusion HCQ can ameliorate paraquat-induced pulmonary fibrosis by inhibiting the PI3K/AKt/mTOR signaling pathway.