Most of the humidity measurement methods that are used in practice both in a field working and in a laboratory analysis usually manipulate average values for a specific standard sample. In this article the measurement system for determining the amount of water in a single grain and in small samples of grains without its destruction is presented. It works on the basis of the wave guide transmitation changes detection when the tested sample is present in it. In the case of a bigger samples analysis the information about statistic parameters of the humidity distribution in a sample is received. The results received for soya bean with a different humidity are presented below.