Abstract: Eleven cases were examined by light and electron microscopy on an ultrastructural basis, they were subclassfied into four types, adenocarcinoumatous, adenosquemous, squanmous, and undifferentiated types. It is suggested that undiffetentated type might represent undiffrerntiated large cell carcinoma and most cases reveal characters of adenocarcinomatous cell which has its origin from adenomatous cell and type II Pneumocyte。