"Green" antiscalants are gaining increased interest because of their environment-friendliness. In this work, various samples of carboxymethyl starch (CMS), with different substitution degrees of carboxymethyl groups and molecular weight were designed and prepared. The structures of these CMS samples were characterized by Fourier transform infrared spectroscopy, H-1 nuclear magnetic resonance, and viscosity. CMS was used as a green antiscalant for the inhibition of the growth and formation of calcium carbonate (CaCO3) scale, as evaluated by a static test in laboratory scale. Apart from the environmental parameters, effects of structural factors of CMS, including the substitution degree of carboxymethyl groups and molecular weight, on its scale-inhibition performance Were extensively studied. Results showed that increased substitution degree of carboxymethyl groups and decreased molecular weight of CMS samples favored the distortion of CaCO3 crystal growth through chelating effects and improved the scale-inhibition efficiency. The morphology and crystal form of CaCO3 scale were characterized by scanning electron microscopy (SEM) and X-ray diffraction (XRD), respectively, to further investigate the scale-inhibition mechanisms of CMS. (C) 2017 Elsevier B.V. All rights reserved.