Photoacoustic　imaging,　a　novel　biomedical　imaging　technique　that　combines　the　advantages　of　optical　imaging　and　acoustic　imaging,　offers　high-resolution　biological　tissue　imaging　to　facilitate　the　observation　of　deeper　imaging　sites.　In　other　words,　it　breaks　the　＂soft　limit＂　of　conventional　optical　bioimaging　techniques.　However,　many　diseases,　especially　in　the　early　stage,　present　no　obvious　photoacoustic　contrast;　therefore,　it　is　crucial　to　identify　effective　exogenous　photoacoustic　contrast　agents.　Here　we　introduce　a　novel　two-dimensional　material,　antimonene　nanoflakes　(AMNFs),　which　demonstrates　great　optical　absorption　from　300　nm　to　900　nm　as　well　as　excellent　photothermal　conversion　efficiency　and　photoacoustic　performance.　This　material　is　expected　to　be　useful　as　a　contrast　agent,　helping　to　achieve　excellent　photoacoustic　imaging　of　ultra-small　tumors　in　vivo.