NOVELTY - The method for the production of biogas from fiber-rich organic material with a high portion of high molecular carbohydrate such as whole plants or whole plants conserved as silage by anaerobic fermentation through microorganisms in a fermenter, comprises treating fiber-rich fermentation remnant discharged before and/or during the fermentation in the fermenter and/or from the fermenter after the gas generation process, with microwaves and then simultaneously heating. Injurious bacteria and fungus are deadened and high molecular organic substances are split into low molecular substances.    USE - The method for the production of biogas from fiber-rich organic material with a high portion of high molecular carbohydrate such as whole plants or whole plants conserved as silage by anaerobic fermentation through microorganisms in a fermenter.    ADVANTAGE - The method ensures simple production of biogas from fiber-rich organic material with high quality and high yield.    DETAILED DESCRIPTION - The method for the production of biogas from fiber-rich organic material with a high portion of high molecular carbohydrate such as whole plants or whole plants conserved as silage by anaerobic fermentation through microorganisms in a fermenter, comprises treating fiber-rich fermentation remnant discharged before and/or during the fermentation in the fermenter and/or from the fermenter after the gas generation process, with microwaves and then simultaneously heating. Injurious bacteria and fungus are deadened and high molecular organic substances are split into low molecular substances. The post-treated fermentation remnants are filled out to anaerobic fermentation again into the fermenter. The strength and frequency of the magnetic field intended for the microwave treatment are adjusted so that the heating of the plants and/or the silaged plants and the losing of the water are limited on a certain measure. The fluid components are separated from the fermentation remnants and only the solid components of the remnants are irradiated with microwaves. The plants or conserved plants for the fermentation are mixed with the fermentation remnants heat treated with the microwave before introducing into the fermenter. The organic material is enzymatically, chemically and/or physically decomposed.