NIR-II　fluorescent　nanoprobes　based　on　inorganic　materials,　including　rare-earth-doped　nanoparticles,　single-walled　carbon　nanotubes,　CdS　quantum　dots　(QDs),　gold　nanoclusters,　etc.,　have　gained　growing　interest　in　bioimaging　applications.　However,　these　nanoprobes　are　usually　not　biodegradable　and　lack　therapeutic　functions.　Herein,　we　developed　novel　NIR-II　fluorescence　(FL)　imaging　and　therapeutic　nanoprobes　based　on　black　phosphorus　QDs　(BPQDs),　which　exhibited　excellent　biodegradability　and　high　tunability　of　size-dependent　optical　properties.　By　adjusting　the　size　of　nanoparticles,　BPQDs　can　specifically　accumulate　in　the　kidney　or　liver.　Importantly,　a　low　dosage　of　BPQDs　can　effectively　protect　tissues　from　reactive　oxygen　species　(ROS)-mediated　damage　in　acute　kidney　and　liver　injury,　which　was　real-time　monitored　by　responsive　NIR-II　fluorescence　imaging.　Overall,　we　developed　novel　NIR-II　emitting　and　therapeutic　BPQDs　with　excellent　biodegradability　vivo,　providing　a　promising　candidate　for　NIR-II　FL　imaging　and　ROS　scavenging.　©　2021　American　Chemical　Society.