The effect of addition of single (shWPI) and double-heated whey proteins polymers (dhWPI) to set yoghurts and its influence on the rheological properties was investigated. The hardness of set yoghurt was investigated by TA-XT2i Texture Analyser. The yoghurt fermentation process was monitored by the oscillatory rheometer for 4 h at 43˚C and next cooling to 4˚C and stored for 3 h. The gelation of yoghurt started up more quickly for shWPI and dhWPI fortified yoghurts in comparison to the control samples. Size–exclusion HPLC indicated that native WPI formed soluble aggregates after heat-treatment. The heating time in polymerisation process affected the content of whey protein polymers/aggregates in the solution. The use of WPI solutions heat treated longer led to the improvement of the rheological properties of set yoghurts, which resulted in the increasing of their hardness. Yoghurts fortified by the 1% of dhWPI and shWPI addition, heated for the same period of time during polymerisation process exhibited similar rheological properties. This indicates that heating time is the main, determinant parameter of the polymerisation process.