Calcium aluminate cement (CAC) bonded corundum based castables were prepared using tabular corundum and activated alumina as the starting materials, CAC as the binder, zinc hydroxide (Zn(OH)2) and basic zinc carbonate (BZC) as the ZnO precursors. The effects of the two ZnO precursors on the phase composition and the microstructure of the CAC bonded corundum based castable matrix specimens were analyzed, and the reasons affecting the hot performance of the castables were studied. The results show that Zn(OH)2 with a smaller particle size (d 50=1.26 μm) is prone to agglomerate during sample preparation and generates ZnAl2O4 spinel grains after firing, hindering the growth of CA6, thus decreasing the mechanical strength of the castables. BZC with a larger particle size (d 50=2.91 μm), which shows a sound dispersity, in-situ generates nano-sized ZnO after firing, and ZnO or Zn2+ diffuses into calcium aluminates, promoting the sintering of CA2 and CA6, thereby enhancing the hot properties of the CAC-bonded corundum based castables.