The influence of brown coal genetic type and method of chemical pre-treatment on its behavior in pyrolysis processes has been shown. An important role of brown coal reductivity in coal thermal decomposition has been ascertained. It has been found that chemical pre-treatment permits variation of the rate of pyrolysis, the yields of pyrolysis products and structure of semi-cokes. (C) 2002 Elsevier Science B.V All rights reserved.