Abstract <p>The study presents a method for grain size analysis of bottom sediments that includes both sieve analysis and grain size measurement by laser diffraction. The laser diffraction method is successfully used worldwide to study the grain size distribution of marine bottom sediments. The aim of the study is to optimize this method for bottom sediments of shelf seas, which are characterized by a variety of sediment input sources. The method can be used to analyze bulk samples, as well as for grain size analysis of sediments after removal of organic matter, biogenic carbonates, and silica. The distortion of the results of the grain size analysis due to presence of a sand fraction in studied samples has been revealed. It is shown that the initial division of the homogenized sample into two subsamples, one subjected to sieve analysis and the other to laser diffraction method, significantly increases its accuracy.</p>