The polyelectrolyte behaviour of poly(vinyl alcohol)‐boric acid complexes is investigated. A plateau is observed in the dependence of pKa on the degree of neutralization, while the HENDERSON‐HASSELBACH plots show two linear regions with different slope related to two different macroconformations. The complexes undergo a transition to an extended rigid conformation when neutralized in aqueous solution determined by decreased flexibility of the chain and charge acquisition.