Studies related to interaction of whole blood with dissolved oxygen with a new analytical method is a continued research interest in the interdisciplinary areas of biomedical, biochemistry and analytical chemistry. There has been significant number of reports for spectroscopic and electrochemical investigation for the interaction of heme/hemoglobin with dissolved oxygen. Indeed, there is no direct study relating to electron-transfer behaviour of whole blood and oxygen reduction reaction. Complex nature of the blood and difficulty in transferring the electron from the buried hemoglobin in the blood cell are the limitations for the observation. Herein, we report, a human whole blood modified electrode system using graphitized mesoporous carbon and Nafion as a matrix for direct-electron-transfer reaction with dissolved oxygen in physiological solution. The blood modified electrode exhibits a specific redox peak at an apparent standard electrode potential, E degrees' = -0.38 V vs Ag/AgCl corresponding to the electron-transfer reaction of hemoglobin-Fe(III)/Fe(II) redox system and shows a mediated oxygen reduction reaction similar to a commercial Hb modified electrode response. Using the new bio-analytical system, interaction between the blood and dissolved oxygen was studied in terms of oxygen reduction reaction (ORR). Cyclic voltammetry, rotating disc electrode and flow injection analysis coupled with a dual electrode system, wherein, blood and MnO2 modified electrode systems are used for signals corresponding to the oxygen reduction and H2O2 oxidation reactions, kinetics and mechanism. As an extension to practical applicability, quantification of dissolved oxygen using the blood modified electrode was demonstrated with result comparable to that of a commercial dissolved oxygen measurement kit.