The electrocatalytic activity of n-type InP porous nanostructures was investigated in terms of their application to amperometric biochemical sensors. The current sensitivities for H2O2 detection were strongly dependent on the structural properties of these porous nanostructures. A sample with deeper pores responsed more sensitively because of the enlarged surface area inside the nanopores. The removal of an irregular top layer also effectively improved the current sensitivity. The conductive porous nanostructures presented here were very promising for the direct amperometric detection of H2O2.