Herein,　oxidized　3,3′,5,5′-tetramethylbenzidine　(oxTMB)　nanobelts　were　developed　to　enhance　the　colorimetric　and　paper-based　sensing　of　H2O2.　It　was　found　that　the　minor　component　of　Fe2+　in　Na2SO4　reagent　could　catalyze　the　oxidization　of　TMB　by　H2O2　into　positively　charged　oxTMB,　which　was　further　assembled　into　dark　blue　oxTMB　nanobelts　via　electrostatic　interaction　with　SO42−.　The　extinction　originating　from　the　absorption　and　scattering　of　oxTMB　nanobelts　was　utilized　to　quantitatively　detect　H2O2　with　a　wide　linear　detection　range　(1.0–300　μM)　and　a　low　limit　of　detection　(0.48　μM).　In　addition,　no　coffee-ring　effect　was　observed　in　the　test　zone　of　the　paper-based　colorimetric　array,　which　was　beneficial　to　judge　the　color　by　naked　eye.　Finally,　the　colorimetric　method　was　applied　to　detect　H2O2　in　contact　lens　care　solution.　This　work　not　only　proposed　a　new　colorimetric　sensing　platform　for　H2O2,　but　also　highlighted　the　minor　component　in　the　reagent　might　influence　the　experimental　result.　©　2024　Elsevier　B.V.