Two cases of chondroblastoma were studied by tissue culture, immunohistochemistry and electron microscopy as to the histogenetic origin of the tumor cells in tissue culture, the tumor cells were epithelioid in shape with plenty cytoplasm. They were arranged loosely with marked contact inhibition of growth. The cells in these two cases were able to survive for two months through 5 passages. By immunohistochemical study, the tumor cells showed strongly positive reaction to S-100 protein and lysozyme but negative reaction to alpha-antichymotrypsin. Under electron microscope, the surface of tumor cells possessed many microvilli. The tumor cells were characterized by obvious nuclear multilobulation and pseudoinclusion with marked margination of chromatin. In the cytoplasm, scanty amount of ERE and Golgi apparatus were seen. All the above findings support that chondroblastoma cells are derived from immature cartilage cells analogous to fetal cartilage. Moreover, some huge bizarre tumor cells were observed during the later stage of culture which has not been reported in the literature so far.