Photothermal　therapy　is　a　new　type　of　tumor　therapy　with　great　potential.　An　ideal　photothermal　therapy　agent　should　have　high　photothermal　conversion　effect,　low　biological　toxicity,　and　degradability.　The　development　of　novel　photothermal　therapy　agents　with　these　properties　is　of　great　demand.　In　this　study,　we　synthesized　boron　quantum　dots　(BQDs)　with　an　ultrasmall　hydrodynamic　diameter.　Both　in　vitro　and　in　vivo　studies　show　that　the　as-synthesized　BQDs　have　good　biological　safety,　high　photoacoustic　imaging　performance,　and　photothermal　conversion　ability,　which　can　be　used　for　photoacoustic　imaging-guided　photothermal　agents　for　tumor　treatment.　Our　investigations　confirm　that　the　BQDs　hold　great　promise　in　tumor　theranostic　applications.