Objective To investigate the pathological characteristics of early lung adenocarcinoma in a mouse model with emphasis of the tumor growth patterns and tumor-bronch's relationship. Materials and Methods Early lung adenocarcinoma was induced in 10 mice by administering 0.2 mL N-methyl-N-nitro-N-nitrosoguanidine (MNNG, 2.0 mg/mL) once weekly for 4 consecutive weeks. The mice were sacrificed at the 100th day. The lung specimens were fixed in 10% formalin solution. One hundred tumors were randomly sampled, embedded in paraffin, cut into 3-μm sections, stained with hematoxylin and eosin (HE) and evaluated by histopathology. Pathological type, location, size, shape, margin, growth pattern and tumor-bronchus relationship of the tumors were assessed. Results One hundred and eighty-seven tumors were found macroscopically in the 10 mice. All of the randomly selected 100 tumors were adenocarcinomas of a size of 0.19 to 1.33 mm (mean size of 0.48 mm). The tumors demonstrated three types of growth pattern: lepidic (n=6), expansile (n=26), and mixed (n=68). Their mean size was 0.34 mm, 0.54 mm and 0.47 mm, respectively. Ninety-six out of the 100 tumors had direct relation with the bronchioles, of which 13% with the conductive bronchioles and 96% with the ventilating bronchioles. There were bronchioles at the center of tumor in 19% of the tumors, at the outer area of tumor in 49% of the tumors, and at the periphery of tumor in 96% of the tumors. Lobulation (33%) and spiculation (35%) of the tumors were formed by the block of bronchioles or by the invasive growth between or along bronchioles. Conclusions Analyzing the pathological growth patterns and tumor-bronchus relationships in early mouse lung adenocarcinomas will help us to better understand the corresponding CT manifestations of human early lung adenocarcinoma.