In thermal desalination process by multistage flash (MSF) desalination, magnesium hydroxide  (brucite) is a major component of the alkaline (or "soft") scale formed at lower temperatures than  the 'hard" calcium sulfate scale. Brucite formation has also been reported during lime softening  process. During the last three decades various additives have been developed to control  precipitation of scale forming salts. This study is focused on the evaluation of synthetic poly(acrylic acids) with functional groups (carboxylic acid, - COOH) which have the potential to act as inhibitors for brucite scale. Two poly(acrylic acids) were tested with molecular weights
(MW) 2,000 (PAA2k) and 6,000 (PAA6k), respectively. They were present in solutions supersaturated with respect to brucite and the spontaneous precipitation was monitored by the solutions electrical conductivity. Both polymers were effective inhibitors of the crystal growth of the supercritical nuclei forming in the solutions.  The effect of the polymers as brucite inhibitors was compared with 1-hydroxyethylidine 1,1-diphosphonic acid (HEDP). The efficiency of inhibition followed the order: HEDP > PAA2k > PAA6k.