Abstract: Coldspray ionization mass spectrometry(CSI-MS) was employed to investigate the influence of solvent surface tension on protein charge-state distributions(CSD). The CSI-MS spectra of three model proteins were obtained in aqueous solutions, containing acetic acid, formic acid and hydrochloric acid, with different solvent surface tension. None of these solvents affects the CSDs of folded proteins as predicted by the Rayleigh-charge model. The protein CSDs in CSI-MS spectra did not seem to be limited by the solvent surface tension.