The tensile and compressive deformation behavior of a peak-aged cast Mg-11Y-5Gd-2Zn-0.5Zr (wt%) (WGZ1152-T6) alloy was investigated at temperatures between 25 and 400 A degrees C (0.33T (m)-0.75 T (m)) and strain rate ranges of 1 x 10(-4) to 1 x 10(-2) s(-1). The tensile strength (263 +/- 9.5 MPa) and compressive strength (246 +/- 9.0 MPa) at 300 A degrees C were 86 and 49 % of those at room temperature (RT), respectively. The alloy showed anomalous positive temperature dependence of tensile strength from RT to 200 A degrees C, while the compressive strength decreased with increasing temperature for all the temperatures studied. The tensile strength and yield stress of the alloy were considerably superior to those of WE54-T6 and AC8A-T6 at 25 to 400 A degrees C. The flow behavior of the alloy can be described by the Garofalo hyperbolic sine constitutive equation at 250-400 A degrees C. For tension, the stress exponent n was 7.7 +/- 0.7 and the activation energy of deformation Q was 274 +/- 10 kJ/mol; for compression, n was 8.7 +/- 0.4 and Q was 367 +/- 6 kJ/mol. The values of n and Q indicate that the dislocation cross slip was the rate-controlling mechanism, which was consistent with the observed short wavy slip traces usually associated with cross slip. The alloy exhibited obvious tension-compression yield asymmetry at RT, and the asymmetry reduced significantly with increasing temperature. The deformation microstructure revealed that twinning was most probably responsible for the asymmetry, and the nonbasal slip and cross slip played an important role in the reduced asymmetry at high temperatures.