In this paper alkali activation of biomass fly ash - an industrial waste and biomass fly ash-metakaolin blends is investigated. Mixtures of biomass fly ash and commercially available metakaolin ARGICAL 1200 were used as solid components. Different molar volumes of NaOH and sodium silicate solutions were used for the preparation of alkali activators. The mechanical strength was determined after 10 days of curing. The concentration of alkali solution and the mix compositions were optimised for the preparation of mortar samples. The mineral and microstructural properties of the alkali activated binders were carried out by X-ray diffraction (XRD), Thermogravimetric/Differential thermal analysis (TG/DTA) and Scanning electron microscopy (SEM) methods. The mortar samples of biomass fly ashes gave a compressive strength of 18 MPa. The metakaolin incorporated samples showed a higher strength. The highest value was obtained for 40% metakaolin incorporated mortars for around 38 MPa. The biomass fly ash metakaolin blend is working well in the alkali activation application resulting in the contribution of both aluminosilicates and hydrated phases formation. (C) 2012 Elsevier Ltd. All rights reserved.