Using a laser profile microscope, we have investigated the internal structures of porous Ni-P electrodeposits grown under fixed current densities to find some properties that characterize the structure of the electrodeposits. The statistical analysis of the digitized microscope images reveals that the porous Ni-P deposits distribute according to a Poisson distribution and have values of the fractal dimension and scaling exponent different from those of the diffusion-limited aggregation model. Another result is that the number of ions at the cathode electrode oscillates at a fundamental frequency, which fact is interpreted by the presence of an oscillatory solution of the electrochemical rate equations in the Ni-P-H system using linearized perturbation equations. (C) 2004 The Electrochemical Society.