Transport separation of molybdenum(VI) through a supported liquid membrane (SLM) was investigated by employing trioctylmethylammonium chloride (TOMAC) as a mobile carrier. The transport behavior of Mo(VI) and W(VI) was greatly dependent on hydrochloric acid and chloride ion concentrations in the feed solution. Molybdenum(VI) was effectively transported together with W(VI) from dilute HCl solutions in the presence of 0.1 M tartaric acid into NaOH stripping solutions. Molybdenum(VI) in high HCl concentration was transported in preference to W(VI). Addition of NaCl to the feed solution reduced the W(VI) transport, and this enhanced the separation of Mo(VI) from W(VI). Lower TOMAC concentration in SLM was favorable for the separation of the two metal ions, and a separation factor (alpha(Mo/w)) of 46 was obtained with 0.1 M TOMAC-SLM.