A video-enhanced pendant bubble tensiometer was employed for the study of the adsorption kinetics of nonionic surfactant C12E6. Two dynamic processes in a quiescent surfactant solution were monitored by measuring the relaxation profiles of surface tension: the adsorption onto a clean air-water interface and the desorption out of an overcrowded interface due to a sudden shrinkage of pendant bubble. In addition, two equilibrium data, equilibrium surface tension gamma(C) and surface equation of state gamma(Gamma), were measured and used for the determination of adsorption isotherm and model parameters. The adsorption of C12E6 was found to be anti-cooperative from the comparison between equilibrium data and the Frumkin isotherm. The controlling mechanism of the adsorption process changes as a function of bulk concentration, indicating a shift of mechanism from diffusion-control at dilute concentrations to mixed diffusive-kinetic control at more elevated bulk concentrations. The desorption process for C12E6 out of an overcrowded interface was also confirmed to be mixed-controlled. Comparison was made for the entire relaxation period of surface tension data and model predictions. Values of the diffusivity and the adsorption/desorption rate constants of C12E6 were evaluated from these dynamic gamma(t) profiles. At the end, the spherical effect on studying surfactant adsorption kinetics was discussed.