SSurfactants or surface-active agents are interesting groups of compounds with characteristic structures, allowing them to decrease the surface tension. A surfactant consists of a hydrophilic head and a hydrophobic tail. Typically, surfactant molecules aggregate into micelles at the critical micelle concentration. In this work, the concept of tautomerism has been successfully used for the determination of the critical micelle concentration of cetyltrimethylammonium bromide using curcumin as a colored probe. The ratio between diketo and keto--enol tautomers of curcumin increases by increasing the concentration of cetyltrimethylammonium bromide above the critical micelle concentration. This ratio can be monitored by measuring the absorbance ratio at A[subscript ?360]/A[subscript ?428]nm. The critical micelle concentration of cetyltrimethylammonium bromide was obtained from the inflection in the curve and was found to be 0.76 mM which agrees with the reported value.