As a half-reaction of electrochemical water splitting, oxygen evolution reaction is a sluggish kinetics process, and thus it is significant to develop highly efficient catalysts. A series of nanocotton-like amorphous ternary Ni-Co-B materials have been successfully prepared by facile electroless deposition method at room temperature and further applied to electrocatalytic oxygen evolution reaction in 1.0 KOH solution. The morphology, composition and element state of as-prepared materials have been characterized by scanning electron microscopy, high resolution transmission electron microscopy, energy dispersive X-ray and X-ray photoelectron spectroscopy. Electrochemical oxygen evolution properties of as-prepared materials have also been systematically investigated by polarization curves, Tafel, EIS and chronoamperometry techniques. When the molar content of nickel salts in raw metal reactants reach to 30%, as-prepared ternary Ni-Co-B electrocatalyst exhibits optimal OER performances with small Tafel slope (113 mV dec−1) and low overpotential of 300 mV (vs. RHE) at current density of 10 mA cm−2. Besides, it presents an excellent electrochemical stability during 55 h chronoamperometry test at constant potential of 1.50 and 1.67 V. The results demonstrate that the proper composition is an important factor to design highly efficient ternary Ni-Co-B electrocatalyst, providing a promising candidate for electrocatalytic oxygen evolution reaction.