Spheroids have attracted much attention in medical research as a tool to understand both disease mechanisms and drug actions in culture. Cell-cell and/or cell-extracellular matrices DDS interactions seen in spheroids allow cells to mimic in vivo cellular microenvironments, resulting in recapitulating in vivo-like cell functions in culture. However, the microenvironments could also function as a barrier to deliver drugs to cells in spheroids. To tackle this drawback, a sulfobetaine polymer was developed as a spheroid-permeable polymer. In this article, the enhanced anticancer activity of anticancer drugs by conjugation with the spheroid-permeable polymer was introduced.