The influence of limestone powder addition on pozzolanic reactivity of calcined clays were investigated. Two clays containing kaolinite and halloysite in their compositions were obtained from different deposits in Turkey and physical, mineralogical, and morphological properties of the raw and calcined clay were characterized. Pozzolanic reactivity of calcined clays with and without limestone powder addition was then examined by means of lime consumption in lime-calcined clay pastes and their isothermal calorimetry as well as strength activity index test. Limestone powder addition enhanced the pozzolanic reactivity of calcined clays by increasing lime consumption and presenting higher heat of reaction released during pozzolanic activity. Limestone addition also provided benefits of reduced water requirement and increased strength activity for calcined clays. Improvements in pozzolanic reactivity and strength activity of calcined clays with limestone powder addition were attributed to nucleation effect provided by limestone particles and also formation of carboaluminate phases during pozzolanic reaction. (C) 2021 Elsevier Ltd. All rights reserved.