<p>Microwaves has been used as an efficient pretreatment for lignocellulosic biomass as well as biomass conversion reactions. Previously, a frequencty at 2.45 GHz has been widely used for microwave reactions, however, the use of adequate microwave frequency is desired for more efficient microwae propagation to each reaction systems. In this paper, we report effects of six different microwave frequencies for conversion of model biomass subsrates (e.g. monosaccharides) with and without polyoxometalate catalysts. The reactions were conducted with waveguide-type (915 MHz, 2.45 GHz, and 5.8 GHz) and coaxial-type reactors (1.7 GHz, 2.0 GHz, 2.7 GHz) equipped with semiconductor microwave generators. The substrates were added to ionic liquid ([BMIM]Cl) or DMSO solvents and reacted under microwave irradiation. The distribution of products varied with different microwave frequencies due to frequency-depednet dielectric property of the catalysts as well as solvents.</p>