The presence of water-soluble polymers affects the interfacial transition zone (ITZ) in polymer-modified cement mortar. Such effects are studied by means of SEM-investigation. Polyvinyl alcohol-acetate (PVAA), Methylcellulose (MC) and Hydroxyethylcellulose (HEC) are applied in a 1 % polymer-cement ratio. The polymers provide an improved dispersion of the cement particles in the mixing water. The tendency of certain water-soluble polymers to retard the flocculation of the cement particles minimizes the formation of a water-rich layer around the aggregate surfaces. They also provide a more uniform distribution of unhydrated cement particles in the matrix, without significant depletion near aggregate surfaces. Both effects enable to reduce the ITZ. The polymers provide a more cohesive microstructure, with a reduced amount of microcracks in the interfacial transition zones.