A Pt nanoparticle modified Pencil Graphite Electrode (PGE) was proposed for the electrocatalytic oxidation and non-enzymatic determination of H2O2 in Flow Injection Analysis (FIA) system. Platinum nanoparticles (PtNPs) electrochemically deposited on pretreated PGE (p. PGE) surface by recording cyclic voltammograms of 1.0 mM of H2PtCl6 solution in 0.10 M KCl at scan rate of 50 mVs(-1) for 30 cycles. Cyclic voltammograms show that the oxidation peak potential of H2O2 shifts from about + 700 mVat bare PGE to + 50 mVat PtNPs/p.PGE vs. Ag/AgCl/ KCl (sat.). It can be concluded that PtNPs/p. PGE exhibits a good electrocatalytic activity towards oxidation of H2O2. Then, FI amperometric analysis of H-2 O-2 was performed under optimized conditions using a new homemade electrochemical flow cell which was constructed for PGE. Linear range was found as 2.5 mu M to 750.0 mMH(2)O(2) with a detection limit of 0.73 mu M (based on Sb/m of 3). As a result, this study shows the first study on the FI amperometric determination of H2O2 at PtNPs/p. PGE which exhibits a simple, low cost, commercially available, disposable sensor for H2O2 detection. The proposed electrode was successfully applied to determination of H2O2 in real sample.