Tillage operations and field traffic may cause soil compaction and alter the pore characteristics in soil. These practices often lead to a reduction in habitable pore space for the soil mesofauna. In the present study the abundance of some euedaphic species of Collembola was investigated under a range of soil bulk densities normally found in agricultural soils. The study was performed using containers with defaunated soil that was compressed to six levels of bulk density in the range 1.02–1.56 g cm−3. One of the following species was added to a separate series: Mesaphorura macrochaeta, Protaphorura armata, and Folsomia fimetaria. The number of individuals and the concentration of ergosterol (used to estimate fungal biomass) were measured after each experiment and related to bulk density and pore size distribution. A series of experiments in which straw was added to the soil in order to increase microbial life was also included. Only F. fimetaria was used in the straw amended series. In the soil experiments without straw amendments, the numbers of M. macrochaeta and P. armata, were significantly reduced when bulk densities increased from 1.37 to 1.47 g cm−3. F. fimetaria did not exhibit any significant response to compaction. The ergosterol concentration was independent of bulk density. When straw was added, the abundance of F. fimetaria declined significantly with increasing bulk density from 1.21 g cm−3. The decline in collembolan numbers was probably due to the decline in coarse pores (>120 μm) because the ergosterol concentration was independent of bulk density. These results show that soil structure and decline in habitable pore space are the key parameters in the abundance of euedaphic Collembola in soil.