Objective Paraquat(PQ) is an effective herbicide which is widely used in agricultural production .PQ poisoning is frequently seen in humans with the lung as the target organ ,but the poisoning mechanisms is not very clear .Studies show that endoplasmic reticulum stress(ERS) is closely associated with poisoning , but there are few reports on the relationship between ER stress and PQ poi-soning.This article was to investigate the effects of ERS-induced apoptosis and total flavonoids from astragalus complanatus (FAC) in a-cute lung injury(ALI) following paraquat poisoning in rats . Methods A total of 30 adult healthy Sprague-Dawley (SD) rats were ran-domly divided into 3 groups:control group, ALI group, ALI+FAC group and ALI+saline group.Biochemical method was applied to de-tect superoxide dismutase (SOD), catalase (CAT) and malondialdehyde (MDA) in lung tisssue,TdT-mediated dUTP nick end labeling (TUNEL) assay in observing lung apoptosis, Western blotting and real-time PCR(RT-PCR) in detecting the changes in expressions of C/EBP homologous peotein (CHOP), activating transcription factor 4 (ATF4) and X-box binding protein 1 (XBP) following ALI, and HE staining in observing the pathological changes of lung tissue . Results Compared with control group , the expression of MDA content was enhanced in ALI group ([3.26 ±0.24] vs [5.04 ±0.36],P<0.01), along with significantly decreased activity of SOD and CAT ([300.26 ±35.69] vs [187.21 ±25.66]), ([5.78 ±1.28] vs [2.15 ±1.12],P<0.01), increased cell apoptosis , upregulated pro-tain level of CHOP ([0.74 ±0.20] vs [0.23 ±0.07],P<0.01) and mRNA expression of ATF4, XBP1 and CHOP.However, FAC sig-nificantly attenuated ALI following PQ , as showed by reduced MDA content , enhanced activity of SOD and CAT , decreased cell apopto-sis, inhibited protain level of CHOP and mRNA expression of ATF 4, XBP1 and CHOP ([5.04 ±0.36] vs [3.99 ±0.27],P<0.01). Furthermore, the activity of SOD and CAT were higher in FAC pretreatment group than those in ALI group ([ 0.74 ±0.20 ] vs [0.42 ±0.11],P<0.01). Conclusion From the research, ERS-induced cell apoptosis is involved in ALI following PQ , and the protec-tive role of FAC in lung tissue following PQ is due to its effect in atten-uating ERS-induced apoptosis .