Thermally induced transition in aqueous solution of 1:1 intermolecular complex formed between cetyltrimethylammonium bromide (CTAB) and o-iodophenol was studied by using a high-sensitive scanning microcalorimeter DASM 4 in the temperature range between 20 and 80 degrees C. A heat capacity peak was observed at temperature around 55 degrees C. The peak temperature depended strongly on the heating rate, indicating highly kinetic nature of the transition, The enthalpy change associated with the transition was found to depend significantly on stored period of the solution at room temperature. These observations were discussed in terms of possible structural change of micellar aggregates in association with the change in flow property of the solution during warming, Origin of slow kinetics of the self-assembly and disassembly processes of the complex in the solution is inferred.