This study describes the effects of the electrolyte pH on phosphorus content, microstructures, and internal stress of Ni-P deposits prepared from a sulfamate bath containing phosphorous acid. Decreasing the pH increases the concentration of nondissociated phosphorous acid in the electrolyte, which results in a monotonic increase of the phosphorus content in the deposits. The increase in phosphorus content decreases the grain size but increases the strength of the (111) texture. Decreasing the pH to about 1.5 can decrease the internal stress dramatically to values close to that of the pure Ni deposited at the same pH. A consistent mechanism of the internal stress evolution in both pure Ni and Ni-P deposits associated with varying the pH is proposed. (c) 2007 The Electrochemical Society.