A WE43 (Mg-4Y-3Nd-0.5Zr, wt%) magnesium-rare earth alloy thin-wall component was fabricated by wire arc additive manufacturing, and its microstructure and mechanical properties were investigated by multiscale characterization, microhardness, and tensile tests. The influences of direct aging (T5) and solid solution+aging (T6) on the microstructure evolution and mechanical properties were studied. Results indicate that the as-deposited WE43 alloy has a uniform equiaxed crystal matrix, with an average grain size of 25.3 μm. Reticulated eutectic structure (α-Mg+Mg₄₁Nd₅/Mg₂₄Y₅) is formed due to Nd and Y element liquid segregation at grain boundaries. Tensile strength of as-deposited alloys is 190 MPa. Peak hardness increases from 74 HV_0.2 to 91 HV_0.2 after T5 aging with persistence of significant eutectic structures. Peak aging hardness is 108 HV_0.2 after T6 treatment, and the eutectic structure is dissolved completely, while a small amount of Mg₂₄Y₅ remains in matrix. Tensile strength of alloys is enhanced to 283 MPa after T6 treatment, but it also induces significant grain growth and reduces the elongation in vertical direction more obviously than in horizontal direction.