By functional plates,16 strains which can produceβ-mannana-se were isolated frnm 28 Bacillus spp.Using a pair of degenerated primers,the conserved fragments ofβ-mannanase gene from the selected strains were amplified by PCR.The obtained nucleotide fragments were sequenced and compared with the homologousβ-mannanase genes in GenBank and a phylogenetic tree was generated.Comparing to the genes codingβ-mannanase published,the cloned nucleotide fragments show the highest sequence identity between 62% and 98%.The genes coding for β-mannanase of Bacillus circulus have low identity while the β-mannanase genes of Bacillus subtilis and other Bacillus spp. have high identity.