Arils of Euporia longana L. was extracted with 80% aqueous MeOH and partitioned successively with EtOAc, n-BuOH and $H_2O$. From the n-BuOH fraction, furan compound was isolated through silica gel column chromatography. The results of physico-chemical data including NMR, MS and IR revealed the compound to be 5-(hydroxymethyl)-2-furfuraldehyde. This compound stimulated GDH I activity by $19.2{pm}0.6$, $41.2{pm}0.9$, $68.4{pm}1.1$, $80.3{pm}0.9$ and $85.9{pm}1.6%$ at in vitro concentrations of 0.005, 0.008, 0.02 and 0.03 %, respectively.