The invention relates to a composition comprising bromadiolone mainly in the form of homo-stereo-isomer of formula 3- [3-(4'-bromo- [1,1 '-biphenyl] -4-yl)-3-hydroxy- 1 -phenylpropyl] -4-hydroxy-2H- 1 - benzopyran-2-one, wherein carbons 1 and 3 of group 3-hydroxy-l- phenylpropyl have the same absolute configuration. The invention also relates to a rodenticide bait and to a method for controlling rodent pests.