Endodextranase D8144 from Penicillium sp. (EC 3.2.1.2.) was immobilized on an epoxy-activated monolithic Convective Interaction Media (CIM®) disk in order to produce isomaltooligosaccharides (IMOS) from Dextran T40 in a continuous IMmobilized Enzymes Reactor (IMER). Enzymatic parameters and structure of IMOS were studied for free and immobilized enzymes. The immobilization efficiency of endodextranase D8144 was about 15.9% (w/w) and the real specific activity was close to 6.5 U mg enz−1. The Km values (4.8 ± 0.2 g L−1) for free and immobilized enzymes were the same, showing the absence of diffusional limitation. Moreover, specific patterns of DPs (Degrees of Polymerization) distributions were observed during the enzymatic hydrolysis by HPAEC-PAD (High Pressure Anion Exchange Chromatography-Pulsed Amperometric Detection). Thus, sought-after sizes of IMOS (DPs 8–10) were generated all over the hydrolysis. Finally, the results showed the high stability of this IMER since a relative enzymatic activity about 78% was measured after 5400 volumes column.