The cathodic behaviour of phosphorous acid on pd、pt、and Ni cathodes were studied by potentiodynamic method. Experimental results showed that the phosphorous acid could be reduced at the cathodes. The reduced product had been confirmed to be hypophosphorous acid by chemical analysis. However, hypophosphorous acid can’t be reduced further to phosphorus at cathodes. Thus we incline to believe that the electrodeposition of Ni—P alloys from phosphorous acid—nickel sulfate solutions is a multi—step process.