The effect of water soluble polymers (WSP) on the shrinkage deformation at an early age is reported in this paper. Commercially available hydroxy propyl methyl cellulose (HPMC) with two different molecular weights was employed in the cementitious composites with various mixing ratios. A restrained shrinkage test was conducted with a steel ring in accordance with ASTM C1581-04. In addition to the steel ring's strain, the surface tension, viscosity, internal relative humidity (RH) and crack propagation were also investigated. The polymer-modified cementitious composites were found to be effective in reducing the crack tendency by extending the age at cracking in comparison to the control mixture. The test results also illustrated that the age at cracking significantly correlated with the restrained strain and the stress development, which were influenced by the relative humidity of the cementitious composite. The higher relative humidity that was maintained in the WSP specimen at an early age was due to the modified pore solution's viscosity. Both the viscosity and the surface tension of the pore solution were two major factors that affected the stress rate. A higher internal relative humidity and a lower surface tension contributed to a smaller stress rate. Nevertheless, the computed crack strain of the WSP showed no relationship to the cracking tendency. (C) 2010 Published by Elsevier B.V.