This case of Japanese big-ear rabbit spontaneous endometrial c ar cinoma is adenocarcinoma .Under optical microscope, the cancer cells arranged as glandular ducts,the lumens of gland were of various size.The cells showed big nucleus and little cytoplasm. Cancer cells have invaded into the muscular layer. Under electron microscope we could see that the cancer cells were ellipitical o r irregular with little mitochondrion and rough surfaced endoplasmic reticulum o r even none.And both were tumefacient. A few primary lysosomes could be seen in some cancer cells.The nuclei were big and various in size .The nuclear membrane was pitted and nucleole was meshed.