Human intestinal maltase (HMA) is an ${alpha}$-glucosidase responsible for the hydrolysis of ${alpha}$-1,4-linkages from the non-reducing end of malto-oligosaccharides. HMA has become an important target in the treatment of type-2 diabetes. In this study, epigallocatechin gallate (EGCG) and EGCG glucoside (EGCG-G1) were identified as inhibitors of HMA by an in vitro assay with $IC_{50}$ of $20{pm}1.0$ and $31.5{pm}1.0{mu}M$, respectively. A Lineweaver-Burk plot confirmed that EGCG and EGCG-G1 were competitive inhibitors of maltose substrate against HMA and inhibition kinetic constants ($K_i$) calculated from a Dixon plot were $5.93{pm}0.26$ and $7.88{pm}0.57{mu}M$, respectively. Both EGCG and EGCG-G1 bound to the active site of HMA with numerous hydrophobic and hydrogen bond interactions.