It is a well established fact that, both pore size and volume govern the density and particle size characteristics of any soil. For clayey soils, higher densities followed by lesser particle size result in low pore volumes. However, not many studies were conducted on how these pore characteristics alter with variations in density and particle size. This paper presents the results of a study conducted to understand the effect of compaction effort on the pore size and pore volume characteristics on two semi-arid expansive clays. These two clays selected represent soils with different degrees of expansivity, particle sizes and mineralogy. Mercury Intrusion Porosimetry tests were conducted to study the pore size characteristics at 100, 95, 90, 85, 80, 75 and 70% of maximum dry density (MDD) at corresponding optimum moisture content values. Both pore volume and pore size were analysed with varying density characteristcs and particle sizes. It was observed that in case of samples conducted at 100% MDD, about 50% of the pores were larger than 0.1 μm and this value increased with reduction in density. The current observations assume practical importance especially in the wake of microbial treatments for soils where the the passage of microbes depends on the pore size and more specifically pore throat size.