The kinetics of particle coarsening at columnar structured. gold electrodeposits immersed in aqueous NaCl containing 0.5 M H2SO4 and plain 0.5 M H2SO4 solutions at 298 K, at a constant potential, has been followed by in situ scanning tunneling microscopy (STM) sequential imaging. For this system large anisotropic gold particles grow at the expense of small ones. The value of r, the particle radius measured for any preset growth direction, increases with time t, the decay time, according to r(4) x t, as predicted by a surface diffusion-controlled coarsening mechanism. Coarsening of gold particles occurs without a significant change in the standard deviation of the gold electrodeposit height. The average surface diffusion coefficient of gold atoms derived from STM imaging data agrees with previously reported data derived from electrochemical measurements.