Objective To establish a mouse model of early lung adenocarcinoma to serve the imaging studies of early lung adenocarcinoma. Methods Two-hundred and ten 4-week old SPF female Kunming mice were randomly divided into 5 experimental groups (40 mice per group) and 1 control group (10 mice). The mice of experimental groups were subcutaneously injected with a dose of 0.2 ml 1-methyl-3-nitro-1-nitroso-guanidine (MNNG) solution in concentration of 2.0 mg/mL weekly for 1, 2, 4, 8, 12 weeks (group A-E), respectively, while the mice of control group was subcutaneously injected with 0.2 mL saline weekly for 12 weeks. Ten mice were randomly sacrificed from each experimental group at the 60th, 80th, 100th and 120th days after initial injection (group A₆₀, group A₈₀, group A₁₀₀, group A₁₂₀; group B₆₀,……and so on), and the bilateral lungs were dissected. The tumor occurrence rate, number and size of lung tumors were observed and recorded. Results 1. The tumor occurrence rate and number of lung tumors were positively proportional to the time and dose of MNNG injection. No tumor was found in any group at the 60th day. 2. At the 80th day, the tumor occurrence rate in the groups A, B, C, D and E was 0, 10%, 30%, 40% and 50%, respectively. The number of tumors in each group was 0, 4, 42, 60 and 81, respectively. The number of tumors smaller than 0.5 mm in diameter was 0, 4, 25, 31 and 40, respectively. 3. At the 100th day, the tumor occurrence rate was 20%, 40%, 100%, 100% and 100%, respectively. The number of tumors was 6, 19, 187, 223 and 301, respectively, and the number of tumors smaller than 0.5 mm in diameter was 5, 16, 132, 124 and 123, respectively. 4. At the 120th day, the tumor occurrence rate was 30%, 50%, 100%, 100% and 100%, respectively. The number of tumors was 30, 124, 302, 351 and 362 per group, respectively. The number of tumors smaller than 0.5 mm in diameter was 21, 98, 123, 140 and 108, respectively. The induced lung adenocarcinomas were confirmed by pathology. Conclusions MNNG solution 0.2 mL (2.0 mg/mL) subcutaneously injected weekly for 4 weeks can produce 100% occurrence rate of lung adenocarcinoma in mice and most tumors are smaller than 0.5 mm in diameter at 100th day after initial injection. It is a most suitable model for imaging studies of mouse early lung adenocarcinoma.