Conformational changes of human carbonic anhydrase II (HCAII(pwt)) adsorbed on silica nanoparticles (with an average diameter of 9 Mn) have been investigated using differential scanning calorimetry (DSC), and in some specific cases also using circular dichroism (CD) and intrinsic tryptophan fluorescence. To relate the observed conformational changes to the denaturation stability and/or chemical properties in solution, two N-terminally truncated variants and two mutants of HCAII(pwt) containing specific single site mutations were also investigated. From the thermal transitions of HCAII(pwt) adsorbed to the nanoparticles we found that this variant forms a state that was distinctly different from both the native and molten globule states in solution. No thermal transition at all was observed for any of the other variants adsorbed on nanoparticles. CD and intrinsic tryptophan fluorescence indicate that these variants attain a molten globule-like state at the surface.