The gene encoding for a novel hydrolase, cyclic α-maltosyl-(1→6)-maltose [CMM, cyclo -{→6)-α-D-Glc p -(1→4)-α-D-Glc p -(1→6)-α-D-Glc p -(1→4)-α-D-Glc p -(1→}] hydrolase (CMMase), was cloned from the genomic library of Arthrobacter globiformis M6 and designated cmmF . The gene consisted of 1,353 bp encoding a protein of 450 amino-acids with a calculated molecular mass of 49,344 Da. The deduced amino-acid sequence showed similarities to cyclodextrinase, maltogenic amylase and neopullulanase. On the other hand, the complete sequence of the α-glucosidase gene ( cmmB ), which encodes an enzyme involved in the degradation of CMM, revealed that the gene consisted of 1,704 bp encoding a protein of 567 amino-acids with a calculated molecular mass of 63,014 Da. The four conserved regions common in the α-amylase family enzymes were also found in CMMase and α-glucosidase, indicating that these enzymes should be assigned to this family. The DNA sequence of 5,675 bp analyzed in this study contained another four open reading frames (ORFs), designated cmmC , cmmD , cmmE and cmmG , downstream of cmmB . CmmC , cmmD and cmmE were expected to encode proteins concerned with incorporation of CMM via cell membrane. CmmG was expected to encode a transcriptional regulator protein. CMMase gene, α-glucosidase gene and another four ORFs formed a gene cluster together with 6-α-maltosyltrasferase gene ( cmmA ) which encodes a CMM-forming enzyme, namely cmmABCDEFG . The results of gene analysis suggested that A . globiformis M6 has a unique starch utilization pathway via CMM.