Delays　in　evaluating　cancer　response　to　radiotherapy　(RT)　usually　reduce　therapy　effect　or　miss　the　right　time　for　treatment　optimization.　Hence,　exploring　timely　and　accurate　methods　enabling　one　to　gain　insights　of　RT　response　are　highly　desirable.　In　this　study,　we　have　developed　an　apoptosis　enzyme　(caspase-3)　activated　nanoprobe　for　early　evaluation　of　RT　efficacy.　The　nanoprobe　bridged　the　nanogapped　gold　nanoparticles　(AuNNPs)　and　the　second　near-infrared　window　(NIR-II)　fluorescent　(FL)　molecules　(IR-1048)　through　a　caspase-3　specific　peptide　sequence　(DEVD)　(AuNNP@DEVD-IR1048).　After　X-ray　irradiation,　caspase-3　was　activated　to　cut　DEVD,　turning　on　both　NIR-II　FL　and　PA　imaging　signals.　The　increased　NIR-II　FL/PA　signals　exhibited　a　positive　correlation　with　the　content　of　caspase-3.　Moreover,　the　amount　of　the　activated　caspase-3　was　negatively　correlated　with　the　tumor　size.　The　results　underscore　the　role　of　the　caspase-3　activated　by　X-ray　irradiation　in　bridging　the　imaging　signals　variation　and　tumor　inhibition　rate.　Overall,　activatable　NIR-II　FL/PA　imaging　was　successfully　used　to　timely　predict　and　evaluate　the　RT　efficacy.　The　evaluation　system　based　on　biomarker-triggered　living　imaging　has　the　capacity　to　guide　treatment　decisions　for　numerous　cancer　types.　©　2021　Wiley-VCH　GmbH