Precise detection of pathologically relevant biomolecules could provide essential information on important intercellular, cellular, and subcellular events for accurate disease diagnosis and staging, thus leading to appropriate treatment recommendation. Activatable nanoprobes are nanoscale objects that can be turned on through specific reactions or interactions with biomolecules of interest, and afford some advantageous properties for improved detection of biomolecules both in vitro and in vivo. In this brief review, we highlight several recent examples in the development of activatable nanoprobes for biomolecule detection.