Alkenes in general are known to undergo addition reactions at lower temperatures and allylic substitution or isomerization at higher temperatures. For example, maleic acid (cis-2-butene-1, 4-dioic acid) is known to undergo isomerization on treatment with Conc. HCl in aqueous medium under reflux condition or upon treatment with aqueous bromine under UV light to form fumaric acid, the thermodynamically more stable trans isomer. Several studies propose a mechanism that involves a carbocation or a free radical intermediate; however, there are limited reports on the possible formation of any addition products under conditions of this study. A mechanism involving allylic substitution may be easily ruled out since there are no allylic hydrogens in maleic acid. A better understanding of the mechanism of the isomerization as may be envisioned by the identification of any addition products is essential and forms the basis of this study. Our preliminary studies indicate the possible addition reaction taking place initially at low temperature followed by rotation leading to isomerization and elimination at higher temperatures. Further reactions at optimum temperature and varying conditions are carried out and preliminary results from the reactions of maleic acid with aq.HCl and aq. bromine under different conditions are compared; the products characterized and the mechanism is discussed.