This work aims at enhancing the workability of Al2O3-MgO castables. Al2O3-MgO castables were prepared using tabular alumina particles (5-3, 3-1, ≤1 mm), tabular alumina fines (≤0.088 mm), fused magnesia (≤1 mm), reactive alumina micropowder (PFR40, PBR, and CL) and calcined alumina micropowder (AC34B5 and CT) as the main starting materials, calcium aluminate cement (Secar71) as the binder, and polycarboxylic acid water reducer WS, FS, and AD as the dispersive agent, respectively. Effects of three dispersive agents addition (0.4 mass% WS, 0.2 mass% FS and 1 mass% AD), two kinds of reactive alumina micropowder addition (PFR40 and PBR), composite alumina micropowder addition (PFR40-AC34B5 and CL-CT, the mass ratio from 9/0 to 3/6) on the flow value, apparent porosity, bulk density, cold crushing strength and cold modulus of rupture of Al2O3-MgO castables were investigated. The results show that: (1) with PBR or PFR40, the castables with 0.4 mass% WS own better performance than those with 0.2 mass% FS or 1 mass% AD; (2) compared with the castables with CL-CT composite powder, the castables with PFR40-AC34B5 composite powder have slightly higher flow value; with the decreasing ratio of PFR40 and AC34B5, or the decreasing ratio of CL and CT, the castables have declined flow value and the dried castable specimens have decreased density but the mildly changed strength; in consideration of the high price of reactive alumina, a proper compositing ratio shall be selected.