The crystal growth rates of calcite in a constant-composition environment were measured in the presence of a magnetic field. The magnetic effect to be influenced by any one of the solution variables, including pH, degree of relative supersaturation (sigma), ionic strength (I), Ca2+ to CO32- ionic activity ratio (R), and superficial velocity (v), was investigated while keeping the other variables constant. The growth rate was suppressed completely in the presence of the magnetic field under low pH and supersaturation the growth rate seemed to increase at high pH and relative supersaturation. A conditions. By contrast, more surprising result is that the magnetic suppression effect on CaCO3 growth was observed except at unity activity ratio. The information gathered in this experiment might be used as a reference for understanding the performance of the anti-scale magnetic treatment device. (C) 2008 Elsevier B.V. All rights reserved.