Cemented coal gangue-fly ash backfill (CGFB) mixtures are utilized as the filling materials for backfilling the underground openings in coal mines, and the freshly prepared CGFB slurries are commonly transported into the gobs through a pipeline. Thus the pipeline transportation of the CGFB slurry becomes one of the most important issues. With the help of a pipe loop system built in laboratory, this paper carries out an experimental study on the transportability and pressure drop of the CGFB slurry through the loop pipe. The effects of solids concentration as well as ratios of coal gangue to fly ash, fly ash to Portland cement and coal gangue to Portland cement on the pressure drop of the loop pipe flow of the fresh CGFB slurry samples are respectively revealed and discussed. The results show that the solid contents and the mix proportions of the coal gangue, fly ash and cement have a significant impact on the transportability and pressure drop of the CGFB slurry in the pipe loop. The obtained results in this study can provide guidance for designing and preparing practical CGFB slurries with favorable transportability, satisfying the required pressure drop through the pipeline. (C) 2015 Elsevier B.V. All rights reserved.