The fragment of pGEM-T easyβ,containing the gene of chaperonin subunitβof Acidianus tengchongensis strain S5,was inserted into the plasmid pET23b with Ndel and BamHI,designated as pET236βand transformed into BL21(DE3)or Rosetta-gami^TMB(DE3) pLysS.The expressed protein was soluble.Expression of the subunitβwas 16.2% of total cell proteins in Rosetta-gami^TMB(DE3)pLysS and displayed both monomer and oligomer.The recombinant subunitβwas purified by means of sonication,heating at 70℃for 10 min,am- monium sulfate precipitation,chromatography on Bio-Gel A-1.5m and DEAE-Sepharose CL-6B. The purified recombinant of subunit β dis-played oligomer on native-PAGE and exhibited weak ATPase activity.