Hydration of Ordinary Portland cement (OPC) in the presence of tartaric acid has been Studied by using different techniques. Calorimetric studies have shown a rapid enhanced heat evolution within 5 min of hydration ill presence of 1.0 wt% tartaric acid with a strong retardation of silicate phase hydration. DSC and X-ray diffraction studies have confirmed the formation of calcium tartarate hydrate in presence of 20.0 wt% tartaric acid. This compound is separated in the form of crystals as identified by SEM studies. I.R. Studies confirmed the interaction of tartaric acid with mineral phases of the cement. The retardation of hydration has been explained on the basis of precipitation of calcium tartarate hydrate at the surface of cement grains.