• Vitamin D (1,25-(OH) 2-vitd3) is a common fat-soluble vitamin in the body. It plays an important role in the growth and development of human bones. • Vitamin D has been reported to inhibit cell proliferation and invasion in some cancers. However, experimental studies on the inhibitory effect of vitamin D on non-small cell lung cancer cells are not very common. • The phosphatidylinositol 3-kinase/protein kinase B/rapamycin target protein pathway (PI3K/Akt/mTOR) plays an important role in the proliferation, metastasis and drug resistance of tumor cells. To investigate the effects of vitamin D on the malignant behavior of A549 and NCI-H1975 tumor cells (proliferation, apoptosis, invasion, metastasis and drug resistance-related proteins) and the activation of the PI3K/AKT/mTOR signaling pathway, in order to evaluate the effect of vitamin D on the therapeutic action of cisplatin. In vitro cell experiments, CCK-8, flow cytometry, transwell, scratches, MTT and Western blot were used to reveal the effect of vitamin D on non-small cell lung cancer (NSCLC), and the expression of PI3K/AKT/mTOR signaling pathway was also detected. In vivo animal experiments, the nude mice were divided into four groups: control group, vitamin D treatment group, cisplatin treatment group and vitamin D + cisplatin combined treatment group. After tumor formation in vitro, tumor volume changes were calculated and tumor growth curves were drawn, collected tumor tissues for pathological sections. Western blot was used to detect the expression changes of drug-resistance related proteins in tumor tissues. Meanwhile, protein expression changes of PI3K/AKT/mTOR signaling pathway in tumor tissues were detected. In vitro experiments confirm Vitamin D can inhibit the proliferation, invasion and metastasis of non-small cell lung cancer cells A549 and NCI-H1975, promoting cell apoptosis, up-regulate the sensitivity of chemotherapy drugs. These effects of vitamin D may be correlated with the PI3K/AKT/mTOR signaling pathway. In vivo animal experiments, the changes in tumor volume, tumor inflammatory infiltration range, expression of drug-resistant related proteins and signaling pathway related proteins in mice were as follows: The vitamin D and cisplatin combined treatment group was significantly smaller than the control group. Vitamin D can inhibit the proliferation, invasion and metastasis of non-small cell lung cancer (NSCLC) cells A549 and NCI-H1975 and promote apoptosis, up-regulate the sensitivity of chemotherapy drugs. The effect of vitamin D on NSCLC cells A549 and NCI-H1975 was correlated with the PI3K/AKT/mTOR signaling pathway. Vitamin D also promotes the therapeutic effect of CDDP. [ABSTRACT FROM AUTHOR]