Disclosed is a BOG treatment system. The BOG treatment system according to the present invention includes a compressor that compresses BOG which is generated in an LNG storage tank of a ship or a floating structure; a heat exchanger that cools the BOG compressed by the compressor through heat exchange with BOG to be introduced into the compressor; expansion means for insulated expansion of the BOG cooled by the heat exchanger; a phase separator that performs gas-liquid separation on the BOG which is insulated-expanded by the expansion means and supplies LNG to the LNG storage tank; and a bypass line that supplies the BOG which is insulated-expanded from the downstream side of the expansion means to the downstream side of the phase separator.
