Abstract: A method of producing a boron-based compound represented by general formula (1) including a first step of reacting lithium, magnesium or a compound containing lithium, a compound represented by general formula (2), and a compound represented by general formula (3): R.sup.2 --Y to produce a borate metal salt represented by general formula (4), and a second step of adding to the borate metal salt an onium halide represented by general formula (5): Z.sup.+ .multidot.X.sup.- to effect ion exchange reaction (the symbols in the formulae have the same meanings as described in the specification).According to the production method of the present invention, a high purity boron-based compound represented by the general formula (1) above useful as a photopolymerization initiator and a light-absorbing decolorizing agent can be obtained in a short time and a high yield as compared with the conventional method.