Article is devoted to sieve holes blocking and describes the impact of the content of blocking particles in the feed on this phenomenon. The process of sieve blocking involves particles of varying size being blocked in sieve holes. This is a phenomenon that significantly decreases the sieving process capacity. The sieve blocking coefficient f is applied for a description of sieve blocking. Blocking particles are the ones which is equal to or slightly larger than the sieve holes. Those particles do not pass through the sieve holes, remain over the sieve and may clog (block) the sieve holes, thus reducing the sieve clearance coefficient. The tests were done using a laboratory vibrator and control sieves, by subsequently sieving mixtures of particulate materials with a different content of blocking particles and different percentage share of the upper- and lower-size fractions. Particulate materials of three model grain shapes were used for the tests: spherical, sharp-edged and irregular. The paper also includes a statistical analysis of the results obtained through experiments and an innovative method for describing sieve holes blocking. The new blocking coefficient specifies the percentage number of blocked sieve holes in relation to the total number of sieve holes. Particle size is a parameter that determines the value of the sieve blocking coefficient in time. An increase in the content of blocking particles in the mixtures results in an increase in the percentage number of blocked sieve holes. The content of individual fractions in the mixture also has a significant impact on the course of sieve holes blocking. Sieving is a very common industrial practice. That is why the subject of this paper is so important.