Intrinsically disordered proteins (IDPs), despite lacking a stable structure, play crucial role in majority of the cellular processes. Casein, a key milk protein, represents this category of proteins, due to its dynamic and flexible structure which contributes towards the nutritional and functional properties of milk. The present chapter summarizes the role of osmolytes (small molecular weight organic molecules generally accumulated by cells to protect against denaturing stresses) in regulating the structure-function integrity of intrinsically disordered casein proteins. Osmolyte - casein interplay is of particular interest as these osmolytes have been found to affect the conformational flexibility and functional properties of casein proteins and thus can affect their overall behavior in the cellular environment. The present chapter delves into this by discussing the unique structural and functional properties of casein IDPs and the influence of osmolytes on their structure, stability, and chaperone activity. Elucidation of the osmolyte effects on the structural-functional integrity of caseins should advance our understanding of the dynamics of protein structure and function in complex biological environments and also offer practical perceptions for their future applications.