The structure and rheology of whey proteins at a concentration of 10 % has been investigated as a function of pH. The turbidity of whey protein isolate (WPI) solutions was measured and DSC thermograms were run on samples at 0.2 pH unit intervals. The structure of heat-set gels prepared from these solutions was investigated by confocal laser scanning microscopy and gel strengths and fracture behaviour was also examined. From the DSC studies the maximum denaturation onset temperature of β-lg under these conditions was found to be 3.4 ± 0.2. A number of pH regions were identified where significant physical changes were found. Differences between the two transition regions between fine-stranded and spherical aggregates have been discussed and potential reason put forward. General trends were identified and an anomalous region at pH 6.2 (possibly related to the Tanford transition) was found in all of the properties of the solutions and gels investigated. This work provides a more detailed investigation into a range of structural and behavioural features of WPI gels over the acidic pH range than is currently available in the literature.