〔Abstract〕 Objective To investigate the effect and mechanism of sex-determining region Y-box transcription factor 4(SOX4) on autophagy in small cell lung cancer(SCLC) cells. Methods Human SCLC cell line NCI-H446 was transfected with small interfering RNA(siRNA) to knockdown SOX4. RT-qPCR and Western blot were used to verify the transfection efficiency. NCI-H446 cells were divided into control group, si-SOX4 group, si-SOX4+oe-Beclin1 group and oe-Beclin1 group. Western blot analysis was performed to detect the ratio of microtubule-associated protein 1 light chain 3(LC3)-Ⅱ/LC3-Ⅰ expression and the expression of Beclin1 and p62 in different groups of cells. The transcriptional regulation of Beclin1 by SOX4 was detected by dual luciferase reporter assay and chromatin immunoprecipitation PCR(ChIP-PCR) assay. CCK-8 assay was used to detect the proliferation ability of NCI-H446 cells in different groups. Flow cytometry was used to detect the apoptosis rate of NCI-H446 cells in different groups. Transwell assay was performed to determine the cell migration and invasion ability in different groups. Results Compared with the control group or the si-NC group, the relative mRNA and protein expression level of SOX4 in si-SOX4 group were down-regulated(P<0.05), and the ratio of LC3-Ⅱ/LC3-Ⅰ protein expression and the relative protein expression level of Beclin1 in si-SOX4 group decreased(P<0.05), the relative protein expression of p62 increased(P<0.05). The relative luciferase activity of Beclin1 WT in the si-SOX4 group was lower than that in the si-NC group(P<0.05); the relative enrichment of Beclin1 promoter in the Anti-SOX4 group was higher than that in the Anti-Ig G group( P<0. 05). Compared with control group,cell proliferation activity decreased,cell apoptosis rate increased,migration number and invasion number decreased in si-SOX4 group( P<0. 05). Compared with the si-SOX4 group,the ratio of LC3-Ⅱ/LC3-Ⅰ protein expression and the relative protein expression of Beclin1 increased in si-SOX4 + oe-Beclin1 group,while the relative protein expression of p62 decreased,cell proliferation activity increased,apoptosis rate decreased,migration number and invasion number increased( P<0. 05). Conclusion Down-regulation of SOX4 can inhibit autophagy,decrease proliferation activity of NCI-H446 cells,and inhibit cell migration and invasion by inhibiting Beclin1 expression.