A fast, simple and effective technique for weed fruit cryo-sectioning is introduced. Highly lignified fruits of 4 weed species that can float on water were selected to be dissected by a cryo-sectioning technique so that the internal structure adaptive to floating could be clearly observed. The method includes six steps: material fixation, pre-treatment, fixing to cold stage, cryo-sectioning, section flattening, stain and observation and photography. The successful application of cryo-sectioning technique to weed fruit anatomy demonstrated its advantage without a long process of softening, dehydration and embedding. The crucial steps of the technique are to select a proper concentration of glycerin, a suitable temperature of freezing and an appropriate way of section flattening. In this study, the better micrographs could be obtained when the weed fruits were pretreated with 15% glycerin.