This study demonstrates that boronic acid-containing polymers coated onto solid support function as synthetic mitogens for mouse lymphocytes. The polymer was synthesized by radical copolymerization of 3-acrylamidophenylboronic acid with dimethylacrylamide (poly(AAPBA-DMAA)). The boronic acid in the trigonal form in the copolymer activated lymphocytes, probably by crosslinkage to glycoprotein moieties on the plasma membrane surface, as in the case of lectin stimulation. A higher concentration of phenylboronic acid on the copolymer surface resulted in greater activation of lymphocytes, suggesting that the number of phenylboronic acid residues per unit area may be a crucial factor in lymphocyte proliferation. The proliferative response of lymphocytes was also affected by the surface wettability, probably due to a difference in the flexibility of polymer strands at the cell-polymer interface.