A new plant peroxidase was isolated from the leaves of guinea grass (Panicum maximum) and partially purified using a biphasic polymer system (poly(ethylene glycol) - ammonium sulfate) followed by size-exclusion chromatography and ultracentrifugation until obtaining a homogeneous extract containing a high peroxidase activity. The novel peroxidase was characterized as having a specific activity of 408 U/mg and a molecular weight of 30 kDa. The pH for its optimum activity was 8.0 and exhibited a high thermostability at 66 °C with a kinact of 8.0 × 10? 3 min? 1. The best substrates for peroxidase from guinea grass are o-dianisidine and 2,2?-azino-bis-(3-ethylbenzthiazoline-6-sulfonic acid). POD from guinea grass was directly immobilized on the surface of a graphene screen printed electrode and cyclic voltammograms in the presence of potassium ferrocyanide ([Fe(CN)6]3 ? / 4 ?) as a redox species demonstrated an increase in the electron transfer process. The graphene- modified electrode exhibits excellent electrocatalytic activity to the reduction of H2O2, with a linear response in the 100 ?M to 3.5 mM concentration range and a detection limit of 150 ?M. The new peroxidase from guinea grass allowed the modification of a graphene electrode providing a potential sensor detection system for determination of H2O2 in real samples with some biomedical or environmental importance.