A number of a-glucosidases from fungi and from other sources also catalyse reaction of transglycosylation, producing a-glucosylated compounds. Recently were described in bacteria new routes involving the conversion of maltose into trehalose by transglycosylation reactions. A constitutive extracellular a-glucosidase from Chaetomium thermophilum var. coprophilum was purified and characterized. Enzyme purification involved DEAE-celulolose, CM-cellulose and Octyl-Sepharose columns. Transglycosylated products were analyzed by TLC. The enzyme exhibited a carbohydrate content of 14% and an apparent molecular mass of 107 kDa, estimated by gel filtration. Analysis by SDS-PAGE revealed two polypeptide bands of 22 and 26 kDa, suggesting that the enzyme was constituted of two subunits. Optima of pH and temperature were 7.0 and 60 ºC, respectively. The enzyme was thermostable up to 20 min when incubated at 55 ºC and exhibited a half-life of 54 and 8 min when incubated at 55 ºC and 60 ºC, respectively. The thermoinactivation profile at 55 ºC or 60 ºC was biphasic, suggesting that the enzyme had two states of conformation, or the presence of isoenzymes. These data were consistent with the two protein bands observed in SDS-PAGE. The enzyme hydrolysed maltose, amylose, starch, maltooligosaccharides and isomaltose, in order of preference. The Km and Vmax values were 0.55 ± 0.04 mM and 34.16 ± 2.73 U/mg protein for maltose and 4.35 ± 0.42mg and 4.40 ± 0.42 U/mg protein for starch. The enzyme exhibited transglycosylation activity producing trehalose and maltooligosaccharides from 5% maltose. At early stages of the transglycosylation reaction trehalose was the predominant product; at later stages maltooligosaccharides were also accumulated. Trehalose inhibited both glycosyl hydrolase and transglycosylase activities. The mechanism of synthesis of trehalose and maltooligosaccharides by the a-glucosidase was not completely elucidated. However, the present results suggested that the enzyme produced trehalose directly from maltose. Support: CAPES and CNPq