Milk casein micelles are a natural colloid but it is still unknown their intimate structure. Their structure and stability determine some biological and technological properties of milk such as digestibility or its ability to form yogurt gels or cheese. The atomic force microscopy (AFM) allows to examine the appearance of micelles adsorbed on a solid surface (model for the interface of fat globules), capturing amazing images at the nanometer scale. It was found that the casein micelles are very sensitive to variations in the environmental conditions but also to the adsorption of the particle on a surface such as that used in this study. At a more acid pH, the micelle structure seems less cohesive, due perhaps to the solubilization of a portion of the calcium phosphate.