CMCase positive clones were screened from Cellulomonas sp. YE-5 and named pCE1, pCE2 and pCE3. Among the positive clones pCE1 was used for this study, because it has the smallest insert and the highest CMCase activity among the 3 clones, and its nucleotide sequence was determined. The CMCase gene in pCE1 was composed of 1071 bp of nucleotides coding 357 amino acids. Computer analysis showed that the pCE1 has 65% sequence homology with the endoglucanase from Cellulomonas fimi.