Communities of purple moor-grass meadows are generally decreasing. Many important problems of classification and phytogeography are connected with them. The main goal of the present study was to evaluate changes in species diversity that took place after mowing of Molinion meadows in Kampinoski National Park was discontinued from 1993 to 2006. Selected Molinion meadows in the park were evaluated in terms of their biological diversity. The data collected represented meadows that were still maintained, as well as meadows that had been abandoned at different times in the past. Biodiversity was evaluated using standard ecological indices and Disturbance Index (Z). In general, the Disturbance Index showed an increase in plant community forms that were abandoned or invaded by alien species. An association that was most like the typical form was seen in well maintained meadows, which suggests that the Disturbance Index continually rises with time after a meadow is abandoned. Ecological strategies and mowing tolerance were determined with the help of the BIOLFLOR database. Numerical classification revealed a highly diverse pattern of variability in the meadows examined. Correlations between ecological indicators and phytocenotic variability in Molinion meadows were also evaluated. Unmanaged meadows were compared to meadows in which meadow conservation management practices were carried out.