Interfacial modification caused by fluctuation or desorption of surfactant during microwave irradiation has been proposed by utilizing the characteristic of microwaves to pass through the oil phase and be absorbed at the liquid. liquid interface. Because of the variety of surfactants, aqueous solutions and oils, the systematization of heat transfer related to irradiation method is required for optimization of interfacial modification. In this study, interfacial tension was measured during pulsed microwave irradiation when a surfactant with a long hydrophilic group was stably adsorbed at the liquid. liquid interface. First, the interfacial modification related to the rapid increase in interfacial tension observed as non-thermal effect of microwaves was discussed in terms of the dimensionless number that our group recently proposed as an indicator of microwave energy concentration at the interface, and the validity of the approach was confirmed. Finally, effective conditions for pulsed irradiation were predicted by use of the dimensionless number.