Quaternary Ni-Co-Cu-P coatings were synthesized on 45 steel substrates by electroless deposition. The chemical composition, crystal structures and corrosion properties of the coatings were investigated by EDX, XRD, SEM, salt spray tests and Tafel polarization curves. The results indicated that Ni-Co-Cu-P coatings were amorphous with the content of 32.66 wt.% Ni, 47.19 wt.% Co and 15.28 wt.% Cu. Spherical clusters with the diameter of 240 ~ 500 nm were distributed uniformly on the coating surfaces and some clusters contained nano-sized poles. The coatings showed visible red rust points after 156 h and were totally failed after 192 h in neutral salt spray tests. Moreover, corrosion resistance of the coatings was much better than that of the 45 steel substrates and Ni-Co-P coatings. In 1.0 wt.% H2SO4 solution, corrosion potential and corrosion current density of the coatings were -0.26 V and 19.17 μA?cm-2 respectively. By increasing the potential, numerous microcracks emerged on the coating surfaces. In 3.5 wt.% NaCl solution, the coatings exhibited an active-passive-transpassive behavior with passive films penetrated by Clˉ and resulted with pin-holes.