Nano silica and polymers are both recognized for causing certain changes to the properties of cement mixtures in both fresh and hardened states, through different mechanisms. While each of these admixtures have individually different influences on those mixtures, incorporating both in a single mix might result in interesting observations, which are the focus of this research. The fresh properties of nano silica incorporating polymer-modified mixtures are investigated in terms of flowability, hydration heat properties, and surface adsorption of the particles. Two types of polymer and three sizes of nano silica colloids are incorporated in cement paste mixtures. It is observed that when introducing both nano silica and polymer, a competitive interaction is likely to occur between them, causing certain changes in the behavior of the resulting mixtures in the investigated fresh properties. Considering surface adsorption, one of the polymers shows a stronger surface adsorption, which explains its remarkable influence on the studied properties of hydration reaction and flowability, compared to the other polymer. (C) 2018 Elsevier Ltd. All rights reserved.