Metal-organic cages (MOCs) are discrete molecular assemblies formed by coordination bonds between metal nodes and organic ligands. The application of MOCs has been greatly limited due to their poor stability, especially in aqueous solutions. In this work, we thoroughly investigate the stability of several Zr-MOCs and reveal their excellent stability in aqueous solutions with acidic, neutral, and weak basic conditions. In addition, we present for the first time a process-tracing study on the postassembly modification of one MOC, ZrT-1-NHv highlighting the excellent stability and versatility of Zr-MOCs as a new type of molecular platform for various applications.