Quantitative measurements of adsorption from solution show up to a 70-fold increase in the adsorption coefficient when a variety of organic acids are adsorbed onto 6 nm compared to 16 nn nanocrystalline titania particles. A Langmuir adsorption model modified to include the dependence of interfacial tension (interfacial free energy) on particle size predicts an increase in the adsorption constant (K-ads) as the crystallite size decreases; in agreement with the experimental results. The increase in K-ads arises predominantly from the increased molar;surface free energy of the nanocrystalline particles. The rapid increase in adsorption as particle size decreases has important implications for understanding and modeling natural and experimental systems.