A polyacrylamide derivative of boric acid has been proposed for staining the cellular glycocalyx. Probes differing in their boric acid residue content and type of fluorescent label were obtained by conjugating fully activated polyacrylic acid with aminophenylboronic acid and amino derivatives of dyes. Maximal glycocalyx staining and, at the same time, minimal penetration inside the living cell were observed with a ∼20 kDa probe containing fluorescein and phenylboronic acid residues at a loading of 30 mol %. The patch-like staining reaches its maximum within a few minutes, is irreversible (the probe does not wash out of the glycocalyx), and partly differs from lectin staining.