In spite of environmental contamination due to the indiscriminate fossil fuel use, energy demand is rapidly increasing globally. The world is focusing on research on clean and renewable energy resources that do not emit pollutants. Among them, hydrogen has been referred to as a rising energy resource because its large energy density and zero carbon footprint. Water electrolysis is considered to be one of the most efficient methods of producing hydrogen in high purity. The water electrolysis is composed of the cathode where hydrogen evolution reaction (HER) occurs and the anode where oxygen evolution reaction (OER) occurs. Pt is well known as a catalyst for good performance in cathode, but there are problems of shortage and high cost. Therefore, there are many studies on non-noble metal, especially about transition metal. In addition, researches on catalysts with heterostructure that have good performance in HER have been conducted. However, some catalysts with heterostructure have the disadvantage of being manufactured over a long period of time at high temperature and high pressure. There is an electrodeposition method to solve this problem. Electrodeposition method has the advantage of adjusting morphology, structure and composition variously by easily controlling variables such as concentration of precursor in deposition bath, deposition time, and voltage, using only a small amount of time and energy.In this study, we fabricated heterostructure MoOx@NiMo catalysts by electrodeposition method. First, NiMo with various ratios was electrodeposited by varying Ni concentration in deposition bath. Secondly, surface of NiMo was etched by applying constant potential. In this way, excess Ni on surface removed and Mo was oxidized to MoOx which plays a crucial role on HER catalytic activity, and heterostructure of core and shell was manufactured easily. The heterostructure of catalyst was confirmed by transmission electron microscopy (TEM). Through X-ray photoelectron spectroscopy depth profile (XPS), core composition was determined. And the effect of the core composition on the intrinsic activity was investigated. After leaching, the Mo oxidation state and crystal structure generated on the surface were scrutinized through TEM. In addition, using XPS, we identified the ratio of Mo oxidation state on the surface and confirmed how the ratio of MoOx affects performance. Consequently, catalyst with Ni/Mo ratio of 2.6 in core showed the highest intrinsic activity, and when more MoO2 is formed on surface, the catalyst showed higher intrinsic activity. Also, HER activity and stability of all catalysts were evaluated in acidic media.