Some 2-methylisoselenochromanium salts were prepared. Proton nuclear magnetic resonance spectra in CDCl3 and electron impact mass spectra showed that the selenonium tosylate (4) and mesylate (5) are selenuranes and that the tetrafluoroborate (2) and triflate (3) are selenonium salts. Their structures at the selenium atom are influenced by their counter anions. Selenonium salts (2-5) reacted with some nucleophiles to give a styrene derivative (6) and methyl phenethyl selenides (7, 9).