Objective: To investigate the clinicopathological features, immunophenotype, molecular characteristics and differential diagnosis of colloid adenocarcinoma. Methods: The clinical and pathological data of 4 cases of pulmonary adenocarcinoma were retrospectively analyzed, and associated literature was reviewed. Results: All 4 patients were elderly men, aged 61-67 years, with a median age of 64 years. Three of them had a history of smoking. The clinical manifestations were non-specific symptoms such as fatigue and cough, or without symptoms. The tumors were located in right upper lobe in 3 cases and right lower lobe in 1 case; 3 cases were peripheral located and 1 case almost occupied the entire lobe. The maximum diameter was 1.6-12.0 cm. The cut surface was grayish white, jelly-like and shiny. Microscopically, the tumor showed abundant mucin pools which destroyed the walls of alveolar spaces. The tumor cells showed goblet or signet-ring morphology, with moderate nuclear atypia and low mitotic rate, presenting singly, in small clusters or micropapillary clusters. Tumor cells floated in the mucin pool and a small number of tumor cells might line the alveolar space. Psammoma bodies could be seen in 2 cases. Immunophenotyping showed that 4 cases expressed CK7 and MUC-1, 1 case expressed CK20, 3 cases expressed TTF-1 and NapsinA（1 diffuse and 2 focal）, 2 cases expressed CDX-2, MUC-2 and Villin, 3 cases expressed MUC5AC. Molecular detection showed KRAS mutation in one case. Conclusions: Pulmonary adenocarcinoma is rarely seen. The pathological diagnosis depends on histopathological examination and immunohistochemical staining. The differential diagnosis includes primary mucinous tumor of lung and metastatic mucinous adenocarcinoma. Most cases of pulmonary adenocarcinoma have a good prognosis, but the presence of non-colloid component, interstitial infiltration and micropapillary structure suggests a worse prognosis.