The isothermal dehydration of poly(acrylic-co-methacrylic acid) (PAM) hydrogel under microwave heating (MWH) was investigated. The isothermal kinetics curves of the PAM hydrogel dehydration at temperature range from 293 K to 333 K were recorded. Based on the differential isoconversion method it was concluded that the microwave dehydration of poly(acrylic-co-methacrylic acid) hydrogel is an elementary kinetics process. Applying the model-fitting method it was established that the kinetics of microwave isothermal hydrogel dehydration can be described by the kinetics model of the phase-boundary controlled process (contracting area). The values of the kinetics parameters (activation energy (E-a) and preexponential factor (lnA)) of the dehydration process under microwave heating are lower than the values for conventional heating (CH). The established influence of MWH on the kinetics of hydrogel dehydration is explained with a specific activation mechanism of water molecules for dehydration and with the increase in the value of the energy of the ground level of the resonant oscillator of water molecule (v=837 cm(-1)) due to the absorption of microwave energy. POLYM. ENG. SCI., 56:87-96, 2016. (c) 2015 Society of Plastics Engineers