In a review of data in the published literature, we found that the effect of temperature on capillary pressure in natural soils increased with decreasing geometric mean soil particle diameter. This observation had implications both for hydrologic modeling and for elucidating the mechanisms that controlled the temperature sensitivity of capillary pressure. Two mechanisms were suggested to explain this observation. The first mechanism proposed that changes in soil mineral particle size resulted in changes in the proportion of hydrophyllic and hydrophobic surfaces, yielding changes in their wettabilities, and temperature effects on capillary pressure. The second mechanism proposed that the observation was due to the effect of soil particle size on disjoining pressure. A model derived from the second mechanism could be fitted to the available data and yielded parameter estimates consistent with current models of disjoining pressure profiles above surfaces.