BACKGROUND As we know, chemotherapy resistance is a critical factor leading to recurrence and metastasis of nonsmall-cell lung cancer (NSCLC). To clarify the key target and potential mechanism of resistance to gemcitabine (GEM) in NSCLC, we selected Gene Expression Omnibus Data Set and statistically analyzed a parent cell group and a GEM-resistant cell group. Results showed that the expression of troponin C1, slow skeletal and cardiac type (TNNC1) in GEM-resistant cells was higher than in parent cells, which implies that TNNC1 was associated with GEM resistance in lung cancer cells. MATERIAL AND METHODS TNNC1 expression level was detected by reverse transcription-quantitative polymerase chain reaction or western blot in GEM-resistant patient serum and cell lines. It could reduce or increase autophagy response and GEM resistance accordingly by inhibition of the short interfering ribonucleic acid or by forced overexpression of TNNC1 viruses in A549 cell line and GEM-resistant cell line (A549/GemR) respectively. Blocking autophagy with 3-methyladenine increased the sensitivity of chemotherapy confirmed by flow cytometry and microtubule-associated protein 1A/1B - light chain 3 punctate assay. What's more, in a loss-of-function model, silencing of forkhead box 03 (FOXO3) in A549/GemR cells could rescue the autophagy weakened by TNNC1. RESULTS TNNC1 promoted GEM chemoresistance of NSCLC by activating cytoprotective autophagy, regulated negatively by FOXO3. This research may provide a completely new strategy for NSCLC treatment. CONCLUSIONS Targeting the TNNC1/FOXO3 signaling pathway in NSCLC may be a novel strategy to combat GEM resistance.