Abstract: Objective:The relationship between the effect of early metabolism in 18F-FDG PET/CT and conventional CT based on the RE -CIST standard to evaluate the best objective response after chemotherapy in patients with non-small cell lung cancer (NSCLC). Meth-ods: We studied 40patients with unresectable locally advanced or advanced NSCLC that were confirmed pathologically. The patients were35years old to 78years old and included 31males and9 females. Three patients have unresectable stage ⅢA, 8 patients have stage ⅢB, 29patients have stage Ⅳ, 12patients have squamous cell carcinoma, and 28patients have adenocarcinoma. The PET/CT for the effect of chemotherapy was evaluated in NSCLC according to the SUV standard (SUVmax reduction > 30% of primary lung can-cer after one cycle of chemotherapy), and the CT for the effect of chemotherapy was evaluated on the basis of NSCLC according to the RECIST standard. The objectives of the study are as follows: compare the differences and consistency between 18F-FDG PET/CT metabol-ic response after the first cycle of chemotherapy and the RECIST best objective response after the first or second cycle of chemothera -py with the paired chi-square test and kappa test; calculate the 18F-FDG PET/CT to predict the best objective response of two cycles of chemotherapy according to RECIST on the basis of NSCLC in terms of sensitivity, specificity, accuracy, positive predictive value, and neg -ative predictive value; compare the differences in SUVmax reduction between the metabolic remission group and metabolic no relief group with the two-sample t-test. All statistical methods were 0. 05for the inspection level, and P<0. 05was considered statistically sig-nificant difference (SPSS 19. 0). Results : Differences were found between the first cycle of chemotherapy for the RECIST best objective response and18F- FDG PET/CT metabolic response ( χ2=5. 063 , P=0. 021 ), and the results had bad consistency (Kappa= 0. 240 , P=0. 085 ). No differences were observed between the second cycle of chemotherapy for the RECIST best objective response and18F-FDG PET/CT metabolic response (χ2=2. 083 , P=0. 146 ); the results had good consistency (Kappa= 0. 413 , P=0. 006 ). The sensitivity, specificity, accura -cy, positive predictive value, and negative predictive value were 82%,61%,70%,61%, and 82%, respectively. The differences in SUV -max reduction between the metabolic remission group and metabolic no relief group with the two-sample t-test were statistically significant ( P<0. 001 ). Conclusion:18F- FDG PET/CT may predict the best objective response to chemotherapy for NSCLC patients. Compared with conventional CT,18F-FDG PET/CT can be an early and accurate way to evaluate the chemotherapy effect in NSCLC.