In the present work, the effect of curing medium on microstructure together with physical, mechanical and thermal properties of concrete containing ZnO2 nanoparticles have been investigated. Portland cement was partially replaced by ZnO2 nanoparticles with the average particle size of 15 nm and the specimens were cured in water and saturated limewater for specific ages. The results indicate that ZnO2 nanoparticles up to maximum of 2.0% produces concrete with improved compressive strength and setting time when the specimens cured in saturated limewater. The optimum level of replacement for cured specimens in water is 1.0 wt%. Although the limewater reduces the strength of concrete without nanoparticles when it is compared with the specimens cured in water, curing the specimens bearing nanoparticles in saturated limewater results in more strengthening gel formation around ZnO2 nanoparticles causes more rapid setting time together with high strength. Accelerated peak appearance in conduction calorimetry tests, more weight loss in thermogravimetric analysis and more rapid appearance of peaks related to hydrated products in X-ray diffraction results, all indicate that ZnO2 nanoparticles could improve mechanical and physical properties of the specimens. (C) 2011 Elsevier B.V. All rights reserved.