Iron(III) protoporphyrin IX (Fe(III)P), adsorbed either on single-walled carbon nanotubes (SWCNT) or on hydroxyl-functionalized SWCNT (SWCNT-OH), was incorporated within a Nafion matrix immobilized on the surface of a graphite electrode. From cyclic voltammetric measurements, performed under different experimental conditions (pH and potential scan rate), it was established that the Fe(III)P/Fe(II)P redox couple involves 1e−/1H+. The heterogeneous electron transfer process occurred faster when Fe(III)P was adsorbed on SWCNT-OH (∼11s−1) than on SWCNT (∼4.9s−1). Both the SWCNT-Fe(III)P- and SWCNT-OH-Fe(III)P-modified graphite electrodes exhibit electrocatalytic activity for H2O2 and nitrite reduction. The modified electrodes sensitivities were found varying in the following sequences: S SWCNT-OH-Fe(III)P =2.45mA/M≈ S SWCNT-Fe(III)P =2.95mA/M> S Fe(III)P =1.34mA/M for H2O2, and S SWCNT-Fe(III)P =3.54mA/M> S Fe(III)P =1.44mA/M> S SWCNT-OH-Fe(III)P =0.81mA/M for NO2 −.