In the present work, polyethylene imine (PEI) is used as dispersant to prepare SiC slurry for aqueous gelcasting. When ammonium persulfate (APS) is used as initiator, PEI accelerates the polymerization of monomers and the solidification of gelcasting slurry at 25 degrees C. The reason is that tertiary amine in the structure of PEI and APS form a redox system as initiator. SiC gelcating slurry with PEI and APS solidifies in 2 min at 25 degrees C, which makes the operation of casting impossible. However, when another initiator, 2, 2'-azobis [2-(2-imidazolin-2-yl) propane] dihydrochloride (AZIP.2HCl), is used, PEI does not accelerate but delays the polymerization of monomers because of the chain transfer. SiC gelcasting slurry in the presence of PEI and AZIP.2HCl has good fluidity and long idle time at 25 degrees C. The slurry can be poured into the mold easily and solidifies in 5 min at 45 degrees C. Therefore, PEI can be used as dispersant with the initiator of AZIP.2HCl in the gelcasting process, while PEI cannot act as dispersant when the initiator is APS.