A theoretical model is developed which describes the adsorption kinetics of the two-dimensional first-order phase transition in an adsorption layer. The theory includes a kinetic model of the phase transition in Langmuir and Gibbs monolayers, the adsorption from bulk solution,:and the dissociation kinetics of bulk micelles. The theory describes well the experimental results of the adsorption kinetics of the amphiphiIe N-dodecyl-hydroxy-butyric acidamide dissolved in the aqueous bulk phase. The inflection point of dynamic surface pressure curves corresponds to the first-order phase transition in the adsorption layer. The rate constants for the 2D aggregation in the adsorption layer and the bulk micelle formation are calculated. The relaxation time of the 2D aggregation is approximately ten times lower than that of the association/dissociation of bulk micelles.