Abstract: Through electron microscopy, it was observed that obvious differences were existed in ultrastructure between cells of young leaf and its callus after ten day's culture in sunflower.Obvious changes were observed in ultrastructure during cell changes and callus formation. There was thinner cytoplasm. Granum lamella of plastid degenerated, so did mitochondria cristae and matrix Mitochondria were joined in chains with each other and distributed around the chloroplasts which also around the periphery of the nucleus, vacuoles became highly enlarged and contained some substances. Groups of membrane-enclosed vesicles were found in some changing cells, cohedion of ribosomes and cytoplasms formed line-or net-shaped structures, The microbodies and dictyosomes disappeared in cells.The nuclei of cells at earlier stage of change did not evidently changed, However, at later stage of callus development, some obvious changes also occurred and the contour of nuclei became unclear.