Abstract: Scanning electron microscopic and transmission electron microscopic observation on long-term-cultured callus of Citrus sinensis cv.Valencia were carried out.The results showed that after the callus incubated on MT basic medium for 20 days, the cells were closely linked, a few fibrils appeared on the rumpled surface of the cells, abundant starch granules and organelles were observed in the cells.When cell incubated on the MT basic medium for 50 days, the surface of the cells rumpled, but the fibrils disappeared, ribosome in the cytoplasm increased but the size of starch granules reduced.The callus incubated in the somatic embryo inducing medium for 20 days led to the formation of protuberance and fibrils, sometimes the fibrils formed network, cytoplasm became a mass, and no obvious organelles, starch granules and plasmodesmata were observed) after 50 days, the fibrils on the surface of the cell disappeared, the bulk of the cells and the gap between them increased, organelles and nucleolus reformed, the ribosome were abundant and formed polyers.