A new breeding technology with cell culture in Porphyra yezoensis was studied, to establish a system of fast breeding with cell engineering in Porphyra. By means of somatic cell isolation and multiple clone technique, 4 pure cell-lines (HA, HB, HC, HD) have been established in Porphyra yezoensis. With purely culturing the cell seedlings and conchocelis filaments of the cell lines, their growth rate and resistance to higher temperature were measured. Among cell line HA, HB, HC, HD, HB was the best for resisting higher temperature (at 19 degrees C, 21 degrees C, 23 degrees C, 25 degrees C). Also the growth rate of HB was faster than others. In 1998-2000, the HB was cultivated at sea field of Haifeng in Qidong County, Jiangsu Province. The yield of HB was higher than that of local cultivar. So the HB might be a good cell line for both resisting higher temperature and faster growth. It showed the breeding with cell culture was a fast breeding method.