AIM: To research the effects of cytidine deaminase (CDA) C435T polymorphism on the long-term effectiveness of gemcitabine in non-small cell lung cancer (NSCLC). METHODS: Enrolled 145 NSCLC patients received gemcitabine-platinum regiments at the Affiliated Hospital of Xuzhou Medical University from August 2016 to February 2019, characteristics recorded such as: age, gender, pathological type, clinical stage (I-IIIA/IIIB-IV) and so on. Followed-up and evaluated according to RECIST1.1, the disease-free survival (DFS), progression-free survival (PFS) and overall survival (OS) was study endpoint. Cases were categorized into wild-type CC and mutant CT/TT group. Kaplan-Meier method and log-rank test were utilized to analyze the relationship between CDA C435T and DFS/PFS/OS. A cox model was implemented to analyze the prognostic factors. RESULTS: In stage I-IIIA, median DFS of CT/TT compared with CC was not obvious (16.8 vs. 35.7 months, P=0.294), same in median OS (54.3 vs. 81.9 months, P=0.256). In stage IIIB-IV, the median PFS in CT/TT was longer than CC (10.4 vs. 5.0 months, P=0.009), the median OS was undifferentiated (16.2 vs. 24.3 months, P=0.087). No difference of overall median OS in CC and CT/TT genotypes was seen (21.5 months vs. 25.3 months, P=0.077). Cox regression model showed CDA C435T polymorphism was an independent factor of PFS in stage IIIB-IV (P=0.019). CONCLUSION: CDA C435T polymorphism shows a function as a prediction influencing PFS of gemcitabine in IIIB-IV NSCLC, CT/TT genotype is significantly prolonged.