Geranium (Pelargonium inquinans Ait) leaves were extracted with $80\%$ MeOH, and partitioned into n-hexane, ethyl acetate, BuOH and $H_2O$ to isolate the anticoagulant principles. The EtOAc fraction was found to be the most active, and was further purified using silica and octadecylisilane column chromatography employing a bioassay-guided fractionation method. The active compound was isolated and identified as $1,2,3,4,6-pentagalloyl-eta-D-glucopyranose$(PGG) (compound I). The isolated anticoagulant significantly prolonged the activated partial thrombin time (APTT) and thrombin time (TT) using normal human plasma. One microgram of $1,2,3,4,6-pentagalloyl-eta-D-glucopyranose$ showed 0.063 heparin units in the APTT and 2.73 heparin units in the TT for anti-thrombosis. This is the first report of the isolation of PGG from geranium plants.