Knowledge of the microscopic structure,including three-dimensional(3-D)size and orientation of the precipitates,is essential to fully understand the mechanical properties of the magnesium alloys and designing the alloys with betterperformance.Analytical TEM with high spatial resolution Offers the simultaneous measurements of 3.D size.structure.orientation,composition of the precipitates from one typical sample along an established crystallographic axis.Besidespopular Burgers orientation relationship(OR),other ORs such as Pitsch-Schrader OR,Crawley OR,Potter OR and anew OR with the form of[0001]a 1.0°from[311]γ and(1120)a 2.0°from(033)γ between the magnesium matrix and theprecipitate γ-Mg17Al12 are identified by TEM imaging and diffraction techniques.As a case study,the thicknesses ofthe individual precipitates with Burgers OR are further measured to be lOO-200 nm through both electron energy-lossspectroscopy and x-ray energy dispersive spectroscopy combining difierential x-ray absorption and extrapolation,whichare in agreement with the overall 3-D size statistic distribution results obtained through analysing various samplesalong various directions.Furthermore,the fabricated wedge-shape structure provides a platform on which to study thedependence of the interfacial strain on the variation of the thickness.