The knowledge of the net calorific value of lignites is of prime importance for the industrial use of lignite. It is straightly dependent on the gross calorific value, the moisture content, and the ash content. Its determination is based on specific equations taking into account the above-mentioned parameters. Due to the high inhomogeneity of lignite and the wide variations of moisture and ash contents, the net calorific value by itself cannot be used as a unique parameter for comparing different lignite qualities. In this project the role of the moisture and ash content on the net calorific value is investigated, indicating the misleading effects on assessing the lignite quality.