Cyclin B gene was cloned from shrimp Metapenaeus affinis using RACE.The results showed that the full-length cDNA of cyclin B gene is 1 667 bp,including 1 209 bp coding sequence,the open reading frame encodes a putative peptide of 402 amino acid.The encoded protein does not contain signal peptides in this sequence.BLAST search has shown that the deduced peptide shared 90% sequence identity with that of Metapenaeus ensis.Gene expression profiling by semi quantitative reverse transcriptase polymerase chain reaction(RT- PCR)demonstrated that cyclin B expression levels are the highest in ovary and muscle,then in thoracic ganglion and heart,but almost no expression in gill,hepatopancreas and eyestalk.The results suggest that cyclin B expression levels may relate to its function as a regulator of cell division during cell cycle.Result of prokaryotic expression showed that,the recombinant protein was expressed with expression plasmid pET32a.At last we got a high quantity of recombinant protein(67 ku)in the optimum induction conditions,when the concentration of IPTG was 0.2 mmol/L for 4 h at 25 ℃ for 32a-MaCB.