A fuel supply system for a ship is disclosed. According to the present invention, the fuel supply system for a ship comprises: a fuel supply line pumping and heating LNG from an LNG storage tank provided on a ship to be supplied to a first engine of the ship with natural gas of 3 to 15 bar; a separator provided on the fuel supply line to separate heavy hydrocarbon components more than or equal to two carbon atoms from the pumped LNG to increase a methane number of the LNG to be supplied to the first engine; and an HHC supply line branched from the fuel supply line at the downstream of the separator to supply the heavy hydrocarbon components separated from the separator to an internal combustion engine of the ship.
