The purpose of this study is to evaluate the active properties of Thuja orientalis leaves for the treatment of diabetic complications. The ethyl acetate fraction showed a significantly higher inhibition both of recombinant human aldose reductase (rhALR2) inhibitory activity and advanced glycation endproducts (AGEs). The detected antioxidants (compounds 1-4) by online-HPLC-$ABTS^+$ method and other three compounds were isolated using preparative RP-HPLC and Sephadex LH-20 column chromatography. Among the seven compounds, compound 4 (quercitrin) which was isolated from ethyl acetate fraction, was found to show inhibition for both forms of rhALR2 and AGEs. This compound also inhibited oxidative stress which was measured by Photochem$^{(R)}$ apparatus. In conclusion, the ethyl acetate fraction from T. orientalis demonstrated antioxidant activity as well as inhibitory effects on rhALR2 and AGEs. Quercitrin was shown to be the active compound and hence could be offered as an active material of standardization for the development of natural products for food or medicines.