In the technologies of green fodder production from freshly harvested grass the moisture content control plays the important role in maintenance of high quality and decrease in losses of prepared fodder. The main field technique of moisture control is the dielectric measuring providing rapidity, comprehensible accuracy, simplicity of use and relatively low cost. The experimental measuring device for investigation of wet grasses dielectric properties based on the capacitive sensor and Agilent 4294А Precision Impedance Analyzer, over the electromagnetic field frequency range of 1-30 MHz, used for measurement of grass moisture content, was presented. Parameters of the flat ring capacitive sensor are studied, and a choice of it was proved. The necessary compacting pressure upon grass samples at calculation of their dielectric characteristics was determined. The problem of conversion the measured by the precision impedance analyzer parameters of a cable with the connected capacitive sensor into parameters of tested material has been solved. The preparation procedure of wet grasses to measuring was developed. The geometrical constant of the sensor was determined in the range of the used frequencies. It was determined the penetration depth of an electromagnetic field of the sensor into the tested material according to which the minimum thickness of the studied material layer under the sensor is limited. Dependences of grasses dielectric permittivity and electrical conductivity in the chosen frequency range were experimentally investigated at various values of moisture content and compacting pressure. By results of researches of dielectric properties of grass plants in 2013-2014 a choice of working frequency of measurements in the range of 10-15 MHz and compacting pressure of the studied grasses of 0.31-0.5 N per square meter created by the device was proved.