A novel polymer amphiphile (1), having the copolymer segment containing phenylboronic acid and tertiary amino groups, formed a stable monolayer on water. From the result of pH dependence of the monolayer, the sp(3) hybridization of boronic acid moiety was presumed to be facilitated by both incorporation of amino group in the copolymer segment and its alignment at the air-water interface. The sugar recognition by this polymer monolayer was achieved even at a pH around 6 and became extremely sensitive compared with that of a monolayer consisting of a monomeric boronic acid amphiphile. The 1 monolayer was found to have an ability to discriminate between linkage isomers of disaccharides, which were estimated as molecular area changes of the monolayer upon addition of saccharides in the subphase.