PURPOSE: To enable stable adsorption treatment of boron by allowing resin for selective adsorption of boron which has been converted to free amine form by the regeneration with alkali soln. to contact with soln. of neutral salt, and converting the free amine part of the resin having function for decomposing neutral salt to a salt loaded form.

CONSTITUTION: Mother body of resin obtd. by haloalkylating styrenic copolymer is aminated with an amine expressed by the formula {wherein (n) is an integer 1W6; R is -CH2-[CH(OH)]m-CH2OH or alkyl group; (m) is zero or an integer ≤6} to obtain resin for selective adsorption for boron; boron in the soln. is adsorbed with the abovedescribed resin. In this process, the resin is regenerated to the free amine form using alkali soln. and the free amine from resin is allowed to contact with soln. of neutral salt to convert the free amine form part of the resin to the form loaded with the neutral salt, which is used for the adsorption treatment. As the result, blocking of hardness component or heavy metal component contained in the soln. due to formation of hydroxides, or elevation of pH of the treated liquid is prevented enabling stable operation of adsorption.