Objective To compare the chemical components among Rhizoma Alismatis of different specifications. Methods Rhizoma Alismatis of 8 different weights were chosen, and then contents of 23-acetate alisol B were determined by HPLC, and infrared spectrometry fingerprint was determined by Fourier transform infrared spectroscopy. Results The contents of 23-acetate alisol B in Rhizoma Alismatis of 8 different specifications were over 0.06%, and had no relation with specification of Rhizoma Alismatis (P>0.05). The similarities of infrared spectrometry fingerprint were above 0.9. Conclusion The chemical components among Rhizoma Alismatis of different specifications were basically the same. Contents of 23-acetate alisol B of Rhizoma Alismatis of 8 different specifications conformed to regulation of China Pharmacopoeia.