Cancer theranostics that combines diagnostic and therapeutic effects into one entity holds promise in precision medicine. Conventional theranostic agents possess always-on imaging signals and cytotoxicity effects and thus poor selectivity or specificity in cancer treatment. To tackle this issue, activatable phototheranostic materials (PMs) have been developed to simultaneously and specifically turn on their optical imaging (fluorescence/self-luminescence) or photoacoustic signals and photothermal/photodynamic effects in response to cancer hallmarks. This review summarizes the recent progress in the design, synthesis and proof-of-concept applications of activatable PMs. The molecular engineering strategy to increase tumor accumulation and enhance treatment efficacy are highlighted. Current challenges and future perspectives in this emerging field are also discussed.