Herein,　a　novel　palladium-doped　graphitic　carbon　nitride　nanosheet　(g-C3N4-PdNPs)　is　reported.　The　prepared　g-C3N4-PdNPs　has　a　6.7　and　14.0　times　higher　peroxidase-like　activity　in　comparison　with　pure　Pd　nanoparticles　(PdNPs)　and　graphitic　carbon　nitride　(g-C3N4)　nanosheets　respectively,　and　can　be　stably　stored　for　3　months.　The　high　peroxidase-like　activity　make　g-C3N4-PdNPs　effectively　catalyze　H2O2-mediation　oxidization　of　3,3,5,5-tetramethylbenzidine　to　generate　a　color　change　from　colorless　to　blue　under　lower　concentration　level　and　shorter　time.　The　g-C3N4-PdNPs　can　be　used　as　peroxidase　mimetic　to　develop　sensitive　and　specific　colorimetric　method　for　the　rapid　detection　of　glucose　in　the　serum,　and　to　fabricate　a　simple　and　cheap　portable　test　kit　for　instrument-free　visual　detection　of　glucose　in　serum.　The　portable　test　kit　possesses　obvious　advantages　such　as　low-cost,　short　detection　time,　tiny　sample　consumption,　excellent　specificity,　and　higher　visual　sensitivity.　The　visual　detection　limit　of　portable　test　kit　is　lower　than　the　glucose　concentration　in　the　serum　of　a　diabetic.　Using　portable　test　kit,　the　glucose　in　serum　can　be　visually　detected　by　bare　eye　observation　within　30　min　with　only　30　mu　L　serum　consumption.　The　success　of　this　study　provided　a　potential　approach　for　low-cost　and　instrument-free　see　diabetes　in　clinical　early　diagnosis.