Abstract: In this study, a Δcrp mutant of Salmonella Choleraesuis C78-1 was constructed by the allelic exchange introduced by the transduction of the pRE112 suicide plasmid and characteristics of the mutant were also determined. Firstly, the upstream and downstream fragements of crp gene were amplified from Salmonella Choleraesuis C78-1 genome and then successively subcloned into suicide plasmid pRE112 to construct the recombinant suicide vector pREΔcrp with 320 bp-deleted crp fragment. Then, the C78-1 Δcrp mutant was constructed through the two-step method introduced by the transduction of recombinant suicide plasmid. The O and H antigens of the mutant was 6,7:C:1,5, identical to the parent C78-1 strain. The mutant was stabile with the recombinant Δcrp gene in vitro. However, fermentation patterns and growth rate of the mutant were differed from that of the parent C78-1 strain, obviously. The mouse lethal test showed that the virulence of the mutant was 750 times lower than C78-1. These results showed that the C78-1 Δcrp mutant was constructed successfully. It is likely that this Δcrp mutant could be adapted to develop attenuated Salmonella vaccine.