The sorption of lead ions from aqueous solution onto peat has been studied. The kinetics of sorption of lead ion are described by a pseudo-second-order model modified with a new parameter, t ₀, included to account for an initial resistance due to the film boundary layer. Analysis of this model has been carried out at various experimental conditions to study the effect of initial lead ion concentration, peat particle size, solution temperature, and agitation speed in an agitated batch system. The pseudo-second-order rate constant, initial sorption rate, and sorption capacity, together with time constant, t ₀, also have been determined and correlated as a function of the system variables.