The local gas holdup of carboxymethyl cellulose (CMC) solution-air system in the annular section of a double-tube bubble column is measured by a probe technique. The local gas holdup decreases with increasing CMC concentration. The empirical equation developed for a water-air system to estimate the maximum gas holdup in the annular section is modified by the relative viscosity of the solution to water. Compared with the experimental results, it is demonstrated that the modified correlation is appliable to a CMC solution-air system.