The objective of this study was to analyze the predictive roles of VEGF/KDR/Ras/MAPK gene expression in patients with advanced non-small-cell lung cancer (NSCLC) treated with bevacizumab plus chemotherapy. Twenty-five patients participating in an open-label phase IV trial (SAiL, MO19390) with available tumor tissues were analyzed. The mRNA expression levels of VEGF, kinase insert domain receptor (KDR), Ras, and mitogen-activated protein kinase (MAPK) in tumor tissues were detected using real-time quantitative PCR methods. The relationships between gene expression and disease control rate (DCR), progression-free survival (PFS), and overall survival (OS) were assessed. Patients with lower Ras expression had a longer PFS and OS than patients with higher expression (median PFS, 9.9 vs 5.5 months, χ(2)=3.944, P=0.047; OS, 19.3 vs 7.1 months, χ(2)=9.384, P=0.002). The PFS and OS of patients with lower and higher MAPK expression exhibited a marginal and significant difference (median PFS, 9.9 vs 5.5 months, χ(2)=3.464, P=0.063; OS, 19.3 vs 9.7 months, χ(2)=5.298, P=0.021), respectively. Multivariate analyses using Cox's proportional hazards model showed that Ras is an independent predictor of OS (χ(2)=9.384, P=0.002). No differences in DCR were found according to Ras expression level. The results indicate that Ras is an independent predictor of OS. Thus, patients with lower Ras expression are most likely to benefit from bevacizumab plus chemotherapy treatment regimen. Patients with higher levels of Ras should receive other inhibitors that target Ras. The results also suggest that gene therapies that decrease RAS expression combined with bevacizumab may improve lung cancer treatment. Although there is a very important implication to patient selection in the target therapy, the data in this study are very preliminary owing to the too small sample size. Therefore, further research involving large numbers of patients and a prospective assessment of low and high RAS mRNA expressions getting the same treatments need to be done before conclusions can be made.