In the present work, we have investigated the electrochemical behavior and electrocatalysis of hemoglobin (Hb) immobilized on a glassy carbon electrode (GCE) modified with a graphenecellulose microfiber (GR-CMF) composite. The GR-CMF composite was characterized by scanning electron microscopy, elemental analysis, and Raman and Fourier transform infrared spectroscopy. Well-defined electrochemical redox characteristics of Hb were observed for Hb immobilized on a GR-CMF composite modified GCE, with a formal potential of-0.306 V and a peak to peak separation of approximately 67 mV. Due to the high biocompatibility of the GR-CMF composite, the electrochemical behavior of the Hb heme redox couple (Fe II /Fe III) was enhanced for Hb immobilized on the GR-CMF composite when compared to Hb immobilized on pristine GR. The heterogeneous electron transfer constant (ks) was calculated as 6.17 s-1 , and is higher than previously reported for Hb immobilized GR supports. The Hb immobilized GR-CMF composite modified electrode was used for the quantification of H2O2 under optimal conditions, and shows a wider linear amperometric response ranging from 0.05 to 926 µM. The limit of detection of the biosensor was 0.01 µM with the sensitivity of 0.49 µAµM-1 cm-2. The biosensor also showed high selectivity in the presence of the range of interfering compounds and exhibits good operational stability and practicality in the detection of H2O2.