Non-small cell lung cancer (NSCLC) accounts for more than 80% of lung cancer. Nowadays, gemcitabine and cisplatin in combination have been adopted as the first-line chemotherapy for patients with NSCLC. This study aimed to monitor early response to combined chemotherapy of gemcitabine plus cisplatin in a mouse model of NSCLC by using 18F-fluorodeoxyglucose and 18F-fluorothymidine small animal positron emission tomography (PET). Lewis lung carcinoma-bearing C57BL/6 mice were treated with gemcitabine-cisplatin or saline. Small animal PET with 18F-FDG and 18F-FLT was performed before (baseline) and after treatment (on Day 3), respectively. Imaging results were confirmed by histopathological studies (hematoxylin and eosin staining, Ki67 staining). Compared to the results in the control group, gemcitabine-cisplatin in the treated group significantly inhibited tumor growth (P<0.05). In the treated group, the maximum standardized uptake value (SUVmax) of 18F-FLT decreased significantly from 0.59±0.05 (baseline) to 0.28±0.05 (Day 3) (P<0.05). There was no significant difference between baseline (4.35±0.46) and that on Day 3 (4.02±0.47) on 18F-FDG SUVmax (P>0.05). The proliferation of tumor assessed by Ki67 staining decreased significantly after treatment of one dose of gemicitabine-cisplatin (P<0.05). The staining of HE showed an increase in necrotic and inflam- matory cells after the treatment. This study demonstrated that the uptake of 18F-FLT reduced more rapidly and signi-ficantly than that of 18F-FDG and was less disturbed by the increase of inflammatory cells after chemotherapy.