A composite of manganese dioxide nanosheet and graphene (MnO2/graphene) has been prepared by co-exfoliation of the manganese dioxide with flower-like nanostructure and graphite in isopropanol. The composite has been characterized by transmission electron microscopy (TEM), X-ray photoelectron spectroscopy (XPS), and scanning electron microscopy (SEM). The results of TEM, XPS, and SEM evidenced that the MnO2/graphene composite with nanosheet structure has been prepared successfully. This composite is further cast on glassy carbon electrode to make up a sensor to detect hydrogen peroxide (H2O2). The range of linear detection for H2O2 is 0.5-237 μM. The detection limit of the sensor is 0.07 μM (S/N=3).