A total RNA was obtained from 5 weeks old SPF chicken spleen cells stimulated by ConA, then cDNA of invariant chain (Ii) gene was cloned from the RNA by reverse transcription (RT)-PCR with a pair of designed primers.The length of this cloned fragment was 669 bp and was identified by a restriction endonuclease cleavage.For sequencing,it was further inserted into plasmid pcDNA3,and showed identical with the chicken Ii gene registered in the GenBank. This fragment was inserted into PGEX-4T-1, a prokaryotic expressive plasmid, and the latter was transferred into the strain BL21. After the bacteria were induced and cultured, expressed protein was separated. A band with 50 000 of molecular weight was observed on SDS-PAGE. All these results suggest that the cloned gene of chicken Ii could be expressed in prokaryotic cells.