Ni-P deposits with phosphorous content ranging from 0 to 15.7wt% were plated onto iron sheet from Watts-type bath containing different amounts of phosphorous acid. The corrosion resistance of the electro-deposited Ni-P alloys was studied by the Corrodkote test, immersion test, electrochemical measurement and scanning electron microscopy (SEM). The results are summarized as follows. (1) Corrosion resistance of the as-deposited Ni-P alloys containing 5.3wt% phosphorous was found to be most inferior in the Corrodkote and immersion test. With increasing phosphorous content in the as-deposited alloy, the corrosion resistance increased. Ni-15.7wt%P alloy showed the most superior resistance. Corrosion resistance of the heat-treated Ni-P alloys increased with an increase in the phosphorous content, and Ni-15.7wt%P alloy showed excellent resistance. (2) Natural corrosion potential of the as-deposited Ni-P alloys containing more than about 10wt% phosphorous showed the more noble potential in the Corrodkote solution. (3) Anodic polarization behavior of the Ni-13.4wt%P in the Corrodkote solution was remarkably different from that of amorphous state (as-deposited) and crystal state (heat-treated), that is, the anodic polarization curve of amorphous state shifted toward more noble potential than that of crystal state.