Endo-β-1,4-glucanase gene (with or without signal peptide coding sequence ) was amplified from Sulfolobus islandicus REY15A genomic DNA with PCR and inserted into the Sulfolobus expression vector pZC2,constructing the recombinant plasmid pZC2-eng-YS and pZC2-eng-WS,respectively.Then the recombinant plasmids were electro-transformed into the host strain S.islandicus E233S (△pyrEF△lacS).After induced by D-arabinose and purified with the Ni2+-nitrilotriacetate column,two obvious protein bands with molecular weight about 43 ku and 41 ku appeared on the SDS-PAGE.The following analysis showed the recombinant protein (ENG-W) without signal peptide does not have endo-β-1,4-glucanase activity.However,the activity of recombinant protein (ENG-SP) with signal peptide was 103.4 U/L.The optimal temperature and pH for the recombinant protein (ENG-SP) was 90℃ and 4.0,respectively.Further research indicated that after incubating at 90 °C for one hour,ENG-SP still had 40% of the highest activity.Mn2+ could increase the activity of ENG-SP by 50%,while Ca2+ could inhibit the activity of ENG-SP by 50%.