Protein B23 is one of the two major protein components in eukaryocytic nucleolus. Previous studies indicate that the cellular content and distribution of protein B23 are correlated with the synthetic rate of ribosomal RNA (rRNA) and cell growth. It is more abundant in tumor and growing cells than in normal resting cells. It may translocate from nucleolus to nucleoplasm after serum deprivation, or after being treated with RNA inhibitors such as actinomycin D, toyocamycin, or doxorubicin. In order to search for the role of protein B23 in cell division, using an anti-B23 monoclonal antibody, we detect the cellular content and distribution of protein B23 in interphase and mitotic HeLa cells, respectively. Two microtubule drugs, colcemid and taxol, are used to arrest the mitotic cells. The results show the cellular content of protein B23 in mitotic cells is much higher than that in interphase cells. The intracellular distribution of protein B23 in mitotic cells is distinguished from that in interphase cells too.