The mode of transglycosylation reaction observed during the action of low-molecular-weigh $eta$-D-glucosidase ($eta$-D-glucoside glucohydrolase, EC3.2.1.21) purified from Trichoderma koningii ATCC 26113 was investigated using $^{1}H$-NMR spectroscopy. The enzyme was purified by the series of procedures including ammonium sulfate precipitation, and fractionations by column chromatographies on Bio-Gel P-150, DEAE-Sephadex A-50, and SP-Sephadex C-50. The final purification was performed by the band eluation after preparative polyacrylamide gel electrophoresis. The enzyme showed its molecular size of 78,000 through the analysis of sodium dodecyl sulfate-polyacrylamide gel electrophoresis and its isoelectric point of 5.80 through the analysis of analytical isoelectric focusing. The H-1 proton resonances were analyzed. After the reaction of the enzyme with cellobiose, the reaction products were separated by high performance liquid chromatography using refractive index detector. H-1 resonances of the products were consisted with those of gentiobiose [$eta$-D-glucopyranosyl--(1,6)-D-glucopyranose], and cellotriose [$eta$-D glucopyranosyl-(1,4)-$eta$-D-glucopyranosyl]-(1,4)-D-glucopyranose] with minor resonances of sophorose [$eta$-D-glucopyranosyl-(1,2)-D-glucopyranose], respectively.