Abstract: Objective: To evaluate the chemotherapy-induced leucopenia (CIL) and treatment outcomes of NP regimen in pa-tients with advanced non-small cell lung cancer(NSCLC). Methods: The chemotherapy consisted of Cisplatin 35mg/m² (Ⅳ,on the first two days) and Vinorelbine 25mg/m² (Ⅳ, on the first and eighth day). Each cycle consisted of 21 days. The pa-tients were classified into three groups: Group A consisted of the patients who had grade 0 leucopenia, group B consisted of the patients who had grade Ⅰ~Ⅱ leucopenia, and group C consisted of the patients who had grade Ⅲ~Ⅳ leucopenia.Indices including response rate(RR), disease control rate(DCR), and time to progression(TTP) were analyzed. Results: Atotal of 128 patients were enrolled. The RR in group A, B and C was 30.8%, 56.8% and 71.4%, respectively (P=0.010).The DCR in group A, B and C was 61.5%, 83.8% and 92.9%, respectively (P=0.009). The median TTP in group A, B and C was 150 days(95% CI: 91-209), 189 days(95% CI: 181-197) and 207 days(95% CI: 172-242), respectively(P=0.009).In those patients who had CIL for at least 10 days, the TTP was longer(P=0.0213). Patients with grade I~II leucopenia and ECOG 0 had longer TTP (P=0.0412). Conclusion: The occurrence of CIL is correlated with RR and TTP in patients with advanced NSCLC treated with Cisplatin and Vinorelbine. CIL can be a biological measure of drug activity and an index for efficacy.