Photothermal　therapy　(PTT)　has　attracted　extensive　attention　in　cancer　treatment.　Heptamethine　cyanine　dyes　with　near-infrared　(NIR)　absorption　performance　have　been　investigated　for　PTT.　However,　they　are　often　accompanied　by　poor　photostability,　suboptimal　photothermal　conversion　and　limited　therapeutic　efficacy.　The　photophysical　properties　of　fluorescent　organic　salts　can　be　tuned　through　counterion　pairing.　However,　whether　the　counterion　can　influence　the　photostability　and　photothermal　properties　of　heptamethine　cyanine　salts　has　not　been　clarified.　In　this　work,　we　investigated　the　effects　of　eleven　counter　anions　on　the　physical　and　photothermal　properties　of　NIR-II　heptamethine　cyanine　salts　with　the　same　heptamethine　cyanine　cation.　The　anions　have　great　impacts　on　the　physiochemical　properties　of　dyes　in　solution　including　aggregation,　photostability　and　photothermal　conversion　efficiency.　The　physical　tuning　enables　the　control　over　the　cytotoxicity　and　phototoxicity　of　the　dyes.　The　selected　salts　have　been　demonstrated　to　significantly　suppress　4T1　breast　tumor　growth　with　low　toxicity.　The　findings　that　the　counterion　has　great　effects　on　the　photothermal　properties　of　cationic　NIR-II　heptamethine　cyanine　dyes　will　provide　a　reference　for　the　preparation　of　improved　photothermal　agents　through　counterion　pairing　with　possible　translation　to　humans.