Calcium carbonate scale inhibition by three inhibitors, polyacrylic acid (PAA), aminotrimethylenephosphonic acid (ATMP) and polyamino polyether methylenephosphonate (PAPEMP), has been investigated by the bubbling method, and the calcium carbonate scales formed in the absence and presence of inhibitors have been examined by SEM and XRD. It was found that ATMP shows "threshold effect" in the inhibition of CaCO3 scale, and the inhibition behavior of PAPEMP is similar to that of PAA: the "threshold effect" is not observed. In the presence of inhibitors, the normal growth of calcium carbonate is disturbed, and in the presence of PAPEMP, the scale morphology is similar to that in the presence of ATMP. The vaterite phase is effectively stabilized kinetically in the presence of PAA; ATMP takes second place, and PAPEMP can hardly stabilize kinetically the vaterite phase.