A stereoselective and effective method for the synthesis of vinyl thioethers has been developed. This method is based on the Michael addition of ethanethiol to various alkynyl ketones using 10 mol% of tributylphosphine as catalyst. Most of alkynyl ketones react with ethanethiol in this system to yield mainly Z-isomer of vinyl thioether adducts, only in one case mainly E-isomer of vinyl thioether adducts was observed.