As a first step to achieve our goal to prepare Ohmic contacts to p-type ZnSe using a conventional deposition and annealing method, the microstructure and chemical composition of the ZnSe surface were analyzed by x-ray photoelectron spectroscopy, reflection high-energy electron diffraction, and reflection electron microscopy. A thin native oxide layer consisting of ZnO and SeOx and adsorbed carbons were observed on the ZnSe surface which was grown by the molecular beam epitaxy technique. Most of the oxide layer was removed by saturated bromine water solution. A strong correlation was observed between the surface composition and the electrical properties measured by a current-voltage method for Ni contacting to the N-doped p-type ZnSe substrates. The turn-on voltage (which corresponds to a breakdown voltage for back-to-back Schottky contacts) was significantly reduced by removing the oxide layer using saturated bromine water solution. The present experiment suggested that the interfacial oxide layer is an effective barrier for the carrier transport through the ZnSe/metal interface.