The gene encoding thermostable beta-galactosidase from Pyrococcus woesei was cloned and expressed in Escherichia coli cells. Furthermore, the obtained recombinant strain was used without additional cell permeabilization as a catalyst for the synthesis of galactosylfructose. The optimum pH and temperature for galactosylfructose production by recombinant cells were 5,4 and 80C, respectively. The highest process productivity (7,6 g/lh) was attained at the cells' concentration of 40 mg/ml of the reaction media, using a substrate containing 10% of lactose and 20% fructose. The transgalactosylation activity during the repeated bath processes was almost unchanged after sixfold application of the cells.