1. The seasonal changes in the structure of orthopteran assemblages in 4 grassland types influenced by different soil humidity were examined. 2. 648 orthopteran samples were collected by sweep netting on 54 sampling sites. Parallel to the insect sampling the microclimate (temperature and vapour content) was measured on 216 occasions. 3. Analyses revealed connections between the community structure parameters of orthopteran assemblages and the microclimatic temperature and vapour content of grasslands. 4. The orthopteran assemblages showed significant differences in their annual structure. 5. The microclimate (especially the vapour content) in the grassland patches showed significant seasonal changes in calcareous fens, drying fens, hayfields, semidry grasslands, which seems to be a determining factor in the adjustment of the spatial pattern and seasonal changes of orthopteran assemblages.