OBJECTIVE： To study the effects of combined decoctions of alismatis rhizoma and curcumae radix and rehmanniae radix praeparata on the decoction amount of acteoside in rehmanniae radix praeparata， and provide reference for studying the effective ingredients of three-drug effect. METHODS： Single decoction-1 （rehmanniae radix praeparata 20 g）， single decoction-2 （alismatis rhizoma 20 g）， single decoction-3 （curcumae radix 20 g）， combined decoction-1 （rehmanniae radix praeparata 20 g， alismatis rhizoma 20 g）， combined decoction-2 （rehmanniae radix praeparata 20 g， curcumae radix 20 g）， combined decoction-3 （alismatis rhizoma 20 g， curcumae radix 20 g） and combined decoction-4 （rehmanniae radix praeparata 20 g， alismatis rhizoma 20 g， curcumae radix 20 g） were respectively taken to prepare dry extracts after extracting by refluxing， HPLC was used to detect the acteoside content and calculate its decoction amount in sample. RESULTS： The decoction amounts of acteoside in single decoction-1， combined decoction-1， combined decoction-2 and combined decoction-4 dry extracts were 0.035 4， 0.022 3， 0.022 8， 0.011 0 mg/g， respectively. Compared with single decoction-1 group， the last 3 groups had statistical significances （P＜0.01）； combined decoction-4 showed lowest decoction amount in three-drug combined decoction group. Acteoside was not detected in the negative control groups （single decoction-2， single decoction-3 and combined decoction-3）. CONCLUSIONS： The decoction amount of acteoside is reduced when alismatis rhizoma， curcumae radix and rehmanniae radix praeparata were decocted t