Treatment of 1-(methylsulfinyl)-2-(phenylethynyl)benzene with 10 mol % of mercury dichloride and 1 equivalent of 2,3-dichloro-5,6-dicyano-1,4-benzoquinone in refluxing benzene gave benzo[b]thiophene in good yields. This method tolerated various functional groups in phenylethynyl moiety, including electron donating groups and electron withdrawing groups. Useing 1-(benzylsulfinyl)-2-(phenylethynyl)benzene as reaction substrate increased the yields of benzo[b]thiophene derivatives. Isotope effect showed that this cyclization reaction belong to Pummerer type cyclization reaction.