Ballability of iron ore concentrates is commonly represented by static index K. However, the agreement between K value and green pellet strength is not good enough, and index K does not take into account the influence of binder on the ballability. This paper established a more reliable evaluation model, which can describe the ballability of iron ore concentrates added with and without binder comprehensively. The functions of two moisture-variables consisted in index K were firstly analyzed, and the results show that molecular moisture content can reflect the particle shape and surface area of iron ore concentrates very well, while capillary moisture content relates linearly with moisture capacity. Then a simple model of natural ballability K-1 was proposed and was proven to be better at describing the natural properties of concentrates than conventional K. On this basis, the effects of binder type and binder dosage on balling performance were further investigated, and index K-1 was improved to evaluate the ballability of the concentrates added with an organic binder. Pelletization of 10 iron ore concentrates added with three carboxymethyl celluloses preliminarily demonstrates that K-1 exhibits a good consistency with green pellet strength at the fixed water saturation. (C) 2015 Elsevier B.V. All rights reserved.