The purpose of this article is to find a mathematical model describing the experimental course of the screen blocking coefficient over time. The process of blocking the sieve holes is unfavourable, since it reduces the flow rate of the lower size fraction through a sieve under scrutiny. A description of the process of sieve holes blocking by blocking grains will provide detailed information on the blocking process. This information may be used for determining the screening process parameters and optimising industrial screening. The obtained results were compared with an analytical description of screen blocking provided by other authors (exponential model). In order to fulfil this purpose a series of experiments was carried out at the Department of Process Equipment of the Lodz University of Technology. Fine-grained material of the graining of 0.1-2.5 mm was screened. The study was conducted, using laboratory sieves. Approximation of numerical data using the function of the specified model was done in Mathcad. After having carried out numerous analyses it was found that the logistic function model is the best one to describe the dependence of the screen blocking coefficient over time. (C) 2014 Elsevier By. All rights reserved.