The influence of heat treatment on the performance of various polymers as iron oxide dispersants in an aqueous system has been investigated. The polymers evaluated include: homo-polymers of acrylic acid, methacrylic acid, maleic acid; co-polymer of, acrylic acid:2-acrylamido-2-methylpropane sulfonic acid; ter-polymers of acrylic acid:2-acrylamido-2-methyl propane sulfonic acid:sulfonated styrene, and acrylic acid:2-acrylamido-2-methylpropane sulfonic acid:t-butylacrylamide. It has been found that all polymers lose performance to a varying degree when exposed to thermal treatment (150°C, 200°C, 20hr). The performance data also suggest that sulfonated styrene containing ter-polymer is a better iron oxide dispersant than the ter-polymer containing 2-acrylamido-2-methylpropane sulfonic acid and tertiary butylacrylamide. In the case of co-polymer of acrylic acid:2-acrylamido-2-methylpropane sulfonic acid, the thermal treatment exhibits strong negative influence on the dispersancy power of the polymer. The results have been explained in terms of loss of 2-acrylamido-2-methylpropane sulfonic acid and t-butylacrylamide in the co- and ter-polymers, as determined by FT-IR and NMR methods, leading to the formation of poly(acrylic acid).