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The tensile deformation behavior of an extruded Mg-1Y (wt.%) sheet was investigated in the temperature range of 25 (RT) to 300 ℃ and at strain rates from 0.001 to 0.1 s-1. Ultimate tensile strength (UTS) decreased by 49.3% from 247.9 ± 5.8 MPa when temperature increased from RT to 300 ℃ at the strain rate of 0.1 s-1. It is interesting to note that the flow behavior of the studied sheet exhibited pronounced strain rate sensitivity even at RT. The UTS at RT decreased by 11.8% as the strain rate decrease from 0.1 s-1 to 0.001 s-1. The flow behavior of the alloy can be described by the Garofalo hyperbolic sine constitutive equation in the temperature range of RT to 250 ℃. The measured stress exponent n was 27.8 ± 8.9, and the activation energy Q was 124.6 ± 6.1 kJ/mol. The Q value implied that deformation was controlled by dislocation climb. At intermediate temperature range (~ 150 - 250 ℃), the sheet exhibited serrated flow behavior, and this phenomenon was pronounced at lower strain rates. Simultaneously, the elongation to failure (EL) decreased anomalously with increasing temperature. The above two deformation features were believed to be closely related to the strong interaction between Y solute atoms and dislocations which is known as dynamic strain aging (DSA). The value of strain rate sensitivity ( m ) increased with increasing temperature. The m increasing from 0.068 to 0.11 at 300 ℃ indicated that the addition of Y resulted in the activation of more slip systems. The deformation microstructure observation revealed that twinning was depressed with temperature, which was consistent with the remarkably increased m values. Dynamic recrystallization (DRX) was observed at 300 ℃, and it was promoted with lower strain rate.