Precise　and　rapid　detection　of　immune　responses　is　critical　for　timely　therapeutic　regimen　adjustment.　Immunomodulation　of　tumor-associated　macrophages　(TAMs)　from　a　protumorigenic　phenotype　(M2)　to　an　antitumorigenic　phenotype　(M1)　is　crucial　in　macrophage-targeted　immunotherapy.　Herein,　we　developed　a　boron　dipyrromethene　(BODIPY)-based　fluorescence　probe　BDP3　to　detect　the　immune　responses　after　immunotherapy　by　monitoring　the　nitric　oxide　(NO)　released　by　M1　TAMs.　With　an　aromatic　primary　monoamine　structure　and　a　p-methoxyanilin　electron　donor　in　the　meso-position,　BDP3　not　only　specifically　activates　stable　and　sensitive　fluorescence　by　NO　via　a　photoinduced　electron　transfer　(PET)　process　but　also　achieves　a　long　emission　wavelength　for　efficient　in　vitro　and　in　vivo　imaging.　Such　NO-induced　fluorescence　signals　of　BDP3　are　validated　to　correlate　well　with　the　phenotypes　of　TAMs　detected　in　macrophage　cell　lines　and　tumor　tissues.　The　distinct　sensing　effects　toward　two　types　of　clinically　used　immunotherapeutic　drugs　further　confirm　the　ability　of　BDP3　for　specific　monitoring　of　the　M1/M2　switch　in　response　to　the　macrophage-targeted　immunotherapy.　By　virtue　of　good　biocompatibility　and　appropriate　tumor　retention　time,　BDP3　could　be　a　potential　fluorescent　probe　for　noninvasive　evaluation　of　the　immunotherapeutic　efficacy　of　macrophage-targeted　immunotherapy　in　living　animals.　©　2023　American　Chemical　Society