Objective To investigate the value of 18F-FLT compared to 18F-FDG in PET/CT diagnosis of nasopharyngeal carcinoma (NPC).Methods Twelve newly biopsy-proven NPC patients (age range:22-62 years) were prospectively enrolled into this study after obtaining patient consent.They underwent 18F-FDG PET/CT first,followed by 18F-FLT PET/CT on the consecutive day before treatment.ROIs were drawn on the primary tumor,involved lymph nodes and normal tissues.Wilcoxon rank sum test was used to compare the uptake differences between 18F-FLT and 18F-FDG for both the primary tumor and metastatic lymph nodes.Results All 12 patients showed increased uptake of 18F-FLT by the primary tumor and metastatic lymph nodes,which were consistent with the findings by 18F-FDG PET/CT.The SUVmax and SUVmean of 18F-FLT in the primary NPC (SUVmax 6.0 ± 2.4,SUVmean 3.6 ± 1.5) were lower than those of 18F-FDG (SUVmax 10.7±5.8,SUVmean 5.8±3.0;Z=-2.589 and-2.353,bothP＜0.05).However,the MTV on 18F-FDG and 18F-FLT PET/CT showed no significant difference (15.9 ±9.2 vs 18.1 ± 11.1,Z=-0.786,P ＞ 0.05).The SUVmax SUVmean and MTV of the metastatic cervical lymph nodes in 6 patients showed no significant difference between the 2 tracers (8.5 ± 6.2 vs 6.4 ± 2.5,5.3 ± 4.2 vs 3.8 ± 1.4,6.5±4.8 vs6.0±4.4; Z=-0.734,-0.734,-0.674,respectively,allP＞0.05).The 18F-FLT uptake in the normal temporal lobe (SUVmax 0.7 ± 0.3) Was significantly lower than that of 18F-FDG (SUVmax 8.3 ±2.7,Z =-3.062,P ＜ 0.01).The skull base involvement by NPC could be better delineated on 18F-FLT PET/CT.Conclusions 18F-FLT PET/CT has comparable diagnostic efficacy for primary NPC and metastatic cervical lymph nodes to 18F-FDG PET/CT.It might be better than 18F-FDG for the evaluation of skull base involvement in NPC patients.