Rodents form a vital component of Free State ecosystems and monitoring them may be a relatively quick and inexpensive method of indicating healthy or unhealthy ecosystem functioning. Using removal trapping, we have studied rodent seasonal abundance, species richness, Shannon diversity, and evenness of rodents in four habitats in the Tussen-die-Riviere Nature Reserve, inspected the most successful sampling method for these habitats, and report on their community structure and how it is related to an Ecological Index (≅ EI value of grassland). Both species richness and Shannon diversity increased significantly with EI value. The indicator species Mastomys coucha occurred at all plots, but contributed the largest proportion of the total captures (ca. 80%) at the plot with lowest EI value. Other results important for small mammal monitoring and collecting are that trap success and species richness was highest in autumn. This study also confirms that four days and nights continuous trapping is essential for the effective sampling of rodent communities in Free State grasslands. Our results partially support expectations that the number of specialist species increases with succession, M. coucha dominance acts as an indicator of habitat disturbance, rodent species richness conforms to Tilman's hump-shaped curve model, and adds to a baseline of diversity indices in a variety of grassland habitats.