AbstractKRASmutation is the most frequent type of genetic mutation in non‐small cell lung cancer (NSCLC), especially in lung adenocarcinoma. However,KRASmutation can affect many biological processes and the mechanisms underlyingKRASmutation‐mediate carcinogenesis in NSCLC have not been fully understood. In this research, we found thatKRASG12Cmutation was associated with the upregulation of T‐LAK cell‐originated protein kinase (TOPK), which is a well‐known serine/threonine MAPK‐like protein kinase implicated in tumorigenesis. The overexpression of TOPK significantly promoted the malignant phenotype of A549 cells, and TOPK silencing impaired the malignant phenotype withKRASG12Cmutation. Moreover, we demonstrated that TOPK level was regulated by MAPK/ERK signalling and the transcription factor Elk1. TOPK was also found to promote the activation of NF‐κB signalling in A549 cells withKRASG12Cmutation via facilitating the phosphorylation of TAK1. In the in vivo tumorigenesis model, the administration of TOPK inhibitor OTS514 enhanced the anticancer effect of 5‐FU, and the combinatory use of OTS514 andKRASG12Cinhibitor AMG510 showed synergistic anti‐tumour effect. These results suggest that KRAS‐TOPK axis contributes to the progression of NSCLC and targeting this axis could synergize with anticancer effect of the existing chemotherapeutics.