The Mekong River flows over 4000km through six different nations in SE Asia. Over 130 fish species are reported to migrate distances up to 1000km. Mekong giant catfish are critically endangered on the IUCN Red List, yet little is known about their migration characteristics. Such information is essential if actions to conserve the fish are to be taken. Over 112 hydroelectric dams are currently in underway in the lower basin, yet limited understanding of migrations makes it impossible to accurately assess the impacts of dams on fish. We have tested a novel technique to track the migrations of Mekong giant catfish using pop-up satellite archival transmitters (PSATs). PSATs are typically applied in marine environments, and to our knowledge this is one of the first studies to use PSATs in a freshwater system or on a Pangasius species. Two hatchery-raised fish were tagged using a new attachment method and held in a small reservoir for a period of four months, at which time the tags were programmed to self-release. During the tagging period we received intermittent signals to the satellite, which was unexpected for a species that is primarily benthopelagic. The location accuracy of the tags was tested through manual upload of the data after self-release, and the fish were examined to determine their physical tolerance for the tagging procedure. The results of the study indicate that this method can provide suitable geolocation information for fish that migrate long distances in large rivers.