The transport of hydrochloric acid across a supported liquid membrane using Aliquat 336 in xylene as a carrier was studied. The effect of carrier concentration (0.1–0.6M) on the transportation of hydrochloric acid with and without phase modifier was investigated. The study indicated that the flux of transportation decreased with increasing carrier concentration in the absence of phase modifier. In the presence of phase modifier, however, the flux increased up to 0.2M carrier concentration and started decreasing afterwards. The transportation behavior of hydrochloric acid with and without phase modifier has been attributed to the tendency of aggregation of the carrier.