A validated analytical method is reported for the analysis of paeoniflorin and albiflorin in Bai Shao (Paeonia lactiflora) as a dried raw herb and commercially prepared dried aqueous extract. The samples were extracted by sonication in methanol and the extract analyzed by LC-photodiode array with identity confirmation by electrospray ionization-tandem MS. A C18 column was used with an acetonitrile-water gradient mobile phase. Paeoniflorin and albiflorin were quantified at 230 nm. Ions with m/z 121 and 327 were produced with the MS detector, using the paeoniflorin precursor ion with m/z 479. For albiflorin, the precursor ion with m/z 479 produced the m/z 121 and 77 ions. The amounts of paeoniflorin and albiflorin found in the raw herb were 33.2 and 1.8 mg/g, respectively; and in the dried aqueous extract, the amounts were 34.8 and 15.7 mg/g, respectively. The LODs for paeoniflorin and albiflorin were 0.37 and 1.39 mg/g, respectively, for the raw herb and 0.25 and 0.06 mg/g, respectively, for the dried aqueous extract.