The effects of radiation on the radicals of agar-agar molecule were studied by measuring the infrared spectra at different radiation doses and times after irradiation. The behaviors of infrared spectra against the radiation were observed as follows. The experimental equations for the infrared spectra were given by a) A = a(log X)2+ b log X+c b) A = b - a log t WhereAis the absorbance ratio of radical stretching vibration of the agar-agar Wm,Xis the radiation dose, f is the elapsed time after irradiation, anda,bandcare adjustable constants.