Both stem cells and cancer cells can proliferate indefinitely. In many case, cancers consist of the cells expressing tissue-specific stem cell markers and the cells expressing differentiation markers. Moreover, it has been revealed that many cancer cells express ATP-binding cassette (ABC) transporters, by which the cells pump out a specific fluorescence dyes as well as anti-cancer drugs. Thus these finding suggest that either cancer cells resemble stem cells or cancers contain stem cell-like cells. Using the common characteristics between brain cancer cells and neural stem cells, several research groups have succeeded to identify stem cell-like brain cancer cells (called “brain cancer stem cells”) in brain tumors and brain cancer cell lines. The brain cancer stem cells, but not the other cancer cells, self-renew, form tumors when transplanted in vivo, and are highly resistant for both anti-cancer drugs and irradiation. Together all, these recent progresses suggest that it is crucial to characterize brain cancer stem cells and identify targets for the therapy.