The structures and corrosion behavior of five electroless Ni-Mo-P alloy deposits with 20 to 25-mu-m thickness were studied. The deposits were prepared by controlling the concentration of sodium molybdate (Na2MoO4), which varies from 0 to 0.01 M. Both amorphous and crystalline structures were obtained by changing the concentration of Na2MoO4. The maximum molybdenum content of 19.4 wt percent was obtained at 0.01 M concentration. These deposits of higher phosphorus and lower molybdenum content showed less weight loss after immersion in acidic neutral and alkaline solutions during corrosion tests. This observation is believed to be correlated with the change from crystalline to amorphous structure.