Abstract: Objective To study the proteomics of Bacillus cereus mutant strains LCT-BC25 and LCT-BC235 by detecting the effect of space environment on them. Methods Space Bacillus cereus mutant strains LCT-BC25 and LCT-BC235 and ground control strain LCT-BC244 were identified with isobaric tags for relative and absolute quantitation(iTRAQ) by mass spectrometry. The detected peptides were reassembled and their functions were analyzed. The proteins with a significantly different expression were selected. Results The majority of the 1 269 possible proteins identified in this study were related with the bacterial metabolism according to the cluster of orthologous groups (COG), gene ontology (GO) and Kyoto encyclopedia of genes and genomes (KEGG).The proteomic analysis showed that the protein levels were up-regulated in space 57 and 8 mutant strains and down-regulated in 77 and 73 ground control LCT-BC244 strain. Conclusion The effect of space environment on Bacillus cereus mutant trains is not directional. Bacillus cereus can adapt to the space environment by adjusting its own metablism. The highly expressed hemolytic enterotoxin protein can influence the health of astronauts.