Interleukin-6 (IL-6) is a multifunctional cytokine that is involved in tumor cell proliferation, apoptosis, and differentiation. The purpose of this study was to evaluate the impact of the single nucleotide polymorphism (SNP) -174G/C in IL-6 on the prognosis and pain tolerance of non-small cell lung cancer (NSCLC) patients. DNA was extracted from the peripheral blood of 434 patients with NSCLC, which was diagnosed by cytology or histology. Polymerase chain reaction-restriction fragment length polymorphism was used to detect the IL-6 -174G/C genotypes and their correlation with survival was analyzed. The IL-6 -174G/C genotypes were high IL-6 production type (G carriers - GG or GC genotypes) and low IL-6 production type (CC genotype). The correlation between the IL-6 SNP and pain level/analgesic use was also analyzed. Survival analysis showed that patients carrying the G allele (CG/GG) had a shorter survival time than patients with the CC genotype. The -174G/C SNP is in the promoter region of the IL-6 gene and may be associated with changes in gene transcription and serum cytokine levels. Presence of the IL-6 -174G/C SNP is significantly correlated with morphine equivalent daily dose. Patients with the CC genotype needed a higher opioid dose than patients with the GG or GC genotypes. In conclusion, we found that the IL-6 -174G/C SNP is closely related to survival, analgesic use and pain tolerance in NSCLC patients. However, it is necessary to further validate the results with a larger patient cohort and elucidate the mechanisms of this SNP.