This study aimed to investigate the effect of lactose on the ageing-induced structural changes through avarying lactose content in whey protein powders. In this scope, four powders differing in their lactosecontent (0.1e16 w/w %) were stored at 40 C and 60 C for up to 3 months and sampled periodically. Asmall variation in lactose content of WPI powders was found to affect the level of structural and functionalchanges during powders ageing. At a higher lactose content (2.6 w/w %), proteins were morerapidly lactosylated and aggregated, with a higher rate than the control WPI powder; whereas at a lowercontent (0.1 w/w %) the rate of lactosylation and aggregation was considerably limited. These resultshighlighted the great contribution of the Maillard reaction during ageing of WPI powders. Reducinglactose content in the WPI powders is a promising way to extend their stability among storage.