An activation of levansucrase-catalysed levan formation by NaCl, KCl and Na2SO4 (0.03-0.7 M) was observed using cell-free extract of Zymomonas mobilis. A sigmoidal response of the rate of levansucrase-catalysed reaction to the sucrose concentration was significantly reduced in the presence of salts the Hill coefficient 2.10 and 1.0-1.2 respectively), possibly, due to the heterotropic activation of levansucrase as an allosteric enzyme.