Purpose: To assess the prognostic role of pre-treatment systemic immune-inflammation index (SII) in advanced, metastasis non-small cell lung cancer patients treated with first-line chemotherapy. Study method: cross-sectional study design was conducted on 51 III-IV stage non-small cell lung cancer patients treated with first-line chemotherapy at Oncology Center of Thai Nguyen National Hospital from 01/01/2017 to 31/12/2018. SII index was calculated using formula: platelet count x neutrophil/lymphocyte count. The optimal cut-off value was calculated by ROC curve. The median overall survival time (OS) were estimated using Kaplan-Meier method. A Log-rank test and Cox-regression model were carried out for univariate and multivariate analyses. Results: 22 patients had high SII (≥1.409) and 29 patients had low SII (<1.409). The median OS time was 23,7 months in low SII group and 13,1 months in high SII group (p<0,05). At multivariate analysis, pre-treatment SII and ECOG-PS were independent prognostic factors for worst OS. Conclusion: Pre-treament SII is independent prognostic factor for advanced non-small cell lung cancer patients treated with first-line chemotherapy.