The influence of solvent donor-acceptor properties and polarity on the rates of decarboxylation of benzisoxazole-3-carboxylate ions is analyzed with the unified solvation model. When the dissolved species is a separated ion pair, solvent polarity decreases the rate. When an equilibrium exists between an ion pair and the dissociated ion pair, solvent polarity and donor strength increase the rate by increasing the extent of dissociation. Hydrogen bonding to the carboxylate functionality causes a significant decrease in rate. When using this probe to measure the solvation properties of solvents, micelles, polymers, or biological assemblies, these different effects must be sorted out to interpret the influence of the medium on the observed rate. The unified solvation model provides a means of sorting out these various contributions.