We have investigated the influence of partial hydrolysis with an immobilized proteinase from Bacillus licheniformis on the thermal gelation of isolated β-lactoglobulin B. Gelation behaviour was determined by dynamic rheological measurements (small deformation) and the gels were characterized with respect to microstructure and water-holding properties. A fine-stranded gel with a complex modulus of ∼ 2000 Pa was formed from β-lactoglobulin (50 g/l in 75 mM-Tris-HCl, pH 7·5). Limited hydrolysis prior to thermal gelation resulted in coarser gels with thicker protein strands and larger pores. Gel structure correlated with its permeability, proton mobility and water-holding capacity. Total gel stiffness increased with low degrees of hydrolysis, but decreased after prolonged hydrolysis. Maximal gel stiffness was 1·5-fold that of gels made from unhydrolysed β-lactoglobulin. This was much lower than the stiffening effect obtained after partial hydrolysis of whey protein isolate, showing that the gel strengthening effect of partial hydrolysis was dependent on the protein composition and/or the hydrolysis and gelation conditions. A mechanism to explain the observed effects of hydrolysis on gelation and gel properties is presented.