Abstract This paper aimed to monitory the dry matter biomass production and carbon stocks of above-and below-ground biomass in five types of grasslands in Slovakia: i) lowland oversowed pasture ii) lowland hay meadows, iii) mesophilous pasture, iv) mountain hay meadows, v) abandoned grassland. Averaged over two cropping seasons the total above-and below-ground biomass differed significantly across the monitored grasslands. It ranged respectively from 2.18 to 7.86 t/ha and from 9.64 to 22.67 t/ha dry matter depending on the pedoclimatic condition and the botanical composition of each grassland type. Consequently, this resulted also in the carbon stocks in above-and below-ground biomass. Generally, the mean carbon stocks were 1.56 t/ha for above-ground biomass (24%) and 4.83 t/ha for below-ground biomass (76%). The botanical composition for all the grassland types was also described. The highest number of plant species (55) was observed in lowland hay meadow located in Slovak Karst, the lowest one (23) for the oversowed grassland located in Eastern Slovak Upland. This monitoring paper showed that semi-natural grassland habitats and improved grasslands as well are an important carbon sink, and they can play a key role in global climate change mitigation.