The invention relates to a method and system for monitoring of particles properties in a stream and the use of such method and system. In particular, the invention concerns sampling of liquids like aqueous suspensions or filtrates that contain solid matter in forest industry, oil and mining industry, as well as in and water treatment, desalination or water reuse processes, and in subsequent measurement of the samples. A sample from a stream of liquid is dyed to stain particles contained in the sample, which is conducted to a first flow chamber having means for causing said sample to be divided into particle populations according to their size or mass. A liquid flow is applied through the first flow chamber to cause at least one particle population to flow into a second flow chamber. The particle populations are measured to produce at least one measurement signal representative of the amount and/or properties of the particles, and processing extract key variables of each particle population and presenting them as an analysis of particle populations or the whole sample in terms of a count and size of particles and/or their hydrophobicity.