Mass spectrometric study on cluster structure of solutions of lithium halides (LiX = LiBr and LiI) in acetonitrile is reported. Solvated ions Li + (CH 3 CN) n , X - (CH 3 CN) n , and salt clusters Li + (LiX) m (CH 3 CN) n and X - (LiX) m (CH 3 CN) n , were observed in the spectra. The mechanism of cluster formation is discussed in terms of a competition between solvation interactions and electrostatic interactions. This helps to explain the differences between clustering in methanol and acetonitrile, since the latter one has much larger dipole moment than the former one. Therefore appearance of solvated clusters, including the solvated salt clusters, is more favourable in methanol solutions' spectra.