Objective To obtain a novel pullulanase with synthetic ability from a microorganism and characterize its substrates specificity. Results A novel pullulanase, PulY103A, from Bacillus megaterium Y103 was purified, characterized and expressed in Escherichia coli. PulY103A contained the signature sequences of type I pullulanases and showed 94.7% identity with a type I pullulanase (BmPul) from B. megaterium WW1210, showing similar molecular weight (110.8 kDa) and optimal pH (6.5). However, PulY103A had an optimal temperature of of 45 degrees C and exhibited relatively higher activity toward amylose (48.3%) compared with pullulan (100%), soluble starch (67.5%), and amylopectin (23.1%). The thin-layer chromatography results showed that the major pullulan hydrolysis products were maltotriose and maltohexaose, which differed from those reported in other pullulanases. On the basis of enzyme specificity, PulY103A was an amylopullulanase, which presented transglycosylation activity by forming alpha-1,4-glucosidic linkages. Conclusions A novel amylopullulanase with transglycosylation activity was characterized. The features of this enzyme suggested its potential to produce maltohexaose.