KRAS mutations are found in 15-25 % of patients with lung adenocarcinoma, and they lead to constitutive activation of KRAS signaling pathway that results in sustained cell proliferation. Currently, there are no direct anti-KRAS therapies available. Therefore, it is rational to target the downstream molecules of KRAS signaling pathway, which are mitogen-activated protein kinase (MAPK) signaling pathway (RAF-MEK-ERK) and PI3K pathway (PI3K-AKT-mTOR). Here, we examined the inhibition of both these pathways alone and in combination and analyzed the anti-proliferative and apoptotic events in KRAS mutant NSCLC cell lines, A549 and Calu-1. Cytotoxicity was determined by MTT assay after the cells were treated with LY294002 (PI3K inhibitor), U0126 (MEK inhibitor), and RAD001 (mTOR inhibitor) for 24 and 48 h. The expression levels of p-ERK, ERK, AKT, p-AKT, p53, cyclinD1, c-myc, p27(kip1), BAX, BIM, and GAPDH were detected by western blot after 6 and 24 h treatment. Although PI3K/mTOR inhibition is more effective in cytotoxicity in A549 and Calu-1 cells, MEK/mTOR inhibition markedly decreases cell proliferation protein marker expressions. Our data show that combined targeting of MEK and PI3K-AKT with mTOR is a better option than single agents alone for KRAS mutant NSCLC, thus opening the possibility of a beneficial treatment strategy in the future.