Directional　solidification　of　Mg-1.5Gd　(wt%)　magnesium　alloy　was　carried　out　to　investigate　the　effects　of　the　growth　rate　on　the　microstructures　under　controlled　solidification　conditions.　A　Bridgman-type　directional　solidification　furnace　with　a　liquid　metal　cooling　(LMC)　technique　was　used　to　solidify　the　specimens,　which　could　provide　steady　state　conditions　with　a　constant　temperature　gradient　(40　K/mm)　at　a　wide　range　of　growth　rate　(10　similar　to　200　mu　m/s).　Results　show　that　the　microstructures　are　cellular,　and　the　relationship　between　cellular　spacing　(lambda)　and　growth　rate　(V)　is　established　in　the　form　lambda=　130.2827V(0.2228)　by　a　linear　regression　analysis,　which　is　in　good　agreement　with　the　calculated　values　by　Trivedi　model.　The　thermodynamics　solidification　path　calculations　by　Scheil　model　and　experimental　observations　confirm　that　the　solidification　microstructure　in　the　alloy　consists　of　primary　alpha(Mg)　phase　and　binary　eutectic　alpha(Mg)+Mg5Gd　phase.　Meanwhile,　the　microsegregation　of　the　alloying　element　predicted　by　the　Scheil　model　agrees　reasonably　with　the　electron　probe　microanalysis　(EPMA)　measurements.