The crystal structure of monohydrated trifolin (kaempferol 3-O-β-D-galactopyranoside) (an important biologically active compound, which was isolated from the aerial part of Consolida oliveriana) has been determined from conventional laboratory X-ray powder diffraction data. Variable counting time technique was used during measurement and crystal structure was solved by means of Monte Carlo algorithm. The final structure was achieved by Rietveld refinement using both constraints and restraints on interatomic bond lengths and angles. © 2010 Wiley-Liss, Inc. and the American Pharmacists Association J Pharm Sci 100:1588-1593, 2011.