The high-temperature deformation mechanism and processing maps of cast Al_0.5CoCrFeMnNi that comprises face centered cubic (FCC) and body centered cubic (BCC) phases (where BCC phase is a minor phase) were studied at temperatures in the range of 1023–1323 K and at strain rates in the range of 10⁻³ to 10¹ s⁻¹. During hot compressive deformation, the hard BCC phase provided nucleation sites for dynamically recrystallized (DRXed) grains in the soft FCC matrix through particle stimulated nucleation (PSN). The PSN-induced DRX occurred by continuous dynamic recrystallization (CDRX) and CDRX accelerated as temperature increased. Due to the effect of PSN, the fraction of DRXed grains was notably higher and the size of the DRXed grain size was considerably smaller in Al_0.5CoCrFeMnNi than those in the equiatomic CoCrFeMnNi with a single FCC phase. The effect of the BCC phase on the fraction of DRXed grains was pronounced even at the high strain rate of 10 s^-1 in the temperature range between 1173 and 1323 K, which is advantageous for the practical use of cast Al_0.5CoCrFeMnNi in the hot-working industry. Solute drag creep appeared at low strain rates and at high temperatures as the rate-controlling deformation mechanism due to the presence of Al solutes in the FCC matrix phase. The activation energy for plastic flow associated with solute drag creep was estimated to be 251 kJ/mol. This value most likely represents the activation energy for the diffusivity of aluminum solutes in Al_0.5CoCrFeMnNi. The solute drag creep behavior could be predicted by the Weertman model, suggesting that Al_0.5CoCrFeMnNi behaves similar to a typical class I type solid solution metal alloy. By adding aluminum to CoCrFeMnNi, the hot workability can be greatly improved according to the processing maps. The power dissipation efficiency notably increases, and the flow instability regime decreases in size.