To construct the retroviral vector containing human interleukin 1 receptor antagonist (IL-1Ra)and to investigate the property of the transfected articular chondrocytes from osteoarthritic patients in vitro. Methods Retroviral vector PLXRN carrying IL-1Ra (PLXRN-IL-1Ra) gene was constructed by inserting IL-1Ra gene at the sites of Sal I and BamH I. The recombinant retroviral plasmid was homologously recombinated in bacterial cells. After screening and ampl ification, the recombinant retroviral plasmid was obtained and transfected into PT67 cells. The repl ication-defective retrovirus PLXRN-IL- 1Ra was packed and ampl ified in the PT67 cells. Viral titer was determined by infecting NIH/3T3 cells with serially diluted viral supernatants produced with a control vector. Experiments were divided into 3 groups: non-transducted group (group A), PLXRN transduction group (group B), PLXRN-IL-1Ra transduction group (group C). Primary articular chondrocytes from osteoarthritic patients were transduced with PLXRN and PLXRN-IL-1Ra.The positive chondrocytes clones, which were G418- resistant, were cultured for 3-4 weeks after being selected by G418. The expression of IL-1Ra mRNA in the chondrocytes was determined by RT-PCR. Levels of IL-1Ra protein synthesis in the supernatants were measured by ELISA. Results Restric tive endonuclease identification and gene sequencing confirmed that the recombinant contained IL-1Ra cDNA．Virus titer could reach 3 × 104 CFU/mL. Primary chondrocytes cultured in vitro were polygonal or spindle and were stained with purple particles by toluidine blue staining. After stable transduction into the chondrocytes the 311 bp fragment of IL-1Ra was detected in group C by semi-quantitative RT-PCR. ELISA showed that IL-1Ra in supernatants of the group A and group B were below the level of detection. The concentrations were（60.47 ± 15.13）ng/L in group C .There were significant differences between gene transduction group and control groups (P lt; 0.05). Conclusion The construction of recombinant retrovirus vector by homologous recombination in bacterial cells can be quickly and easily performed. Stable and effective expression of IL-1Ra can be achieved by transduction with retroviral vectors in osteoarthritic articular chondrocytes, indicating potential util ity in gene therapy for osteoarthritis．