Water hyacinth (Eichhornia crassipes) is a cause of great concern in terms of environmental and agricultural impacts in many parts of the world. Phytochemical investigation of water hyacinth led to the isolation of six new phenylphenalenes, 2,3-dihydro-3,9-dihydroxy-5-methoxy-4-phenyl-1H-phenalen-1-one (1), 2,3-dihydro-8-methoxy-9-phenyl-1H-phenalene-1,4-diol (2), 2,3-dihydro-4,8-dimethoxy-9-phenyl-1H-phenalen-1-ol (3), 2,3-dihydro-9-(4-hydroxyphenyl)-8-methoxy-1H-phenalene-1,4-diol (4), 2,6-dimethoxy-9-phenyl-1H-phenalen-1-one (5), and 7-(4-hydroxyphenyl)-5,6-dimethoxy-1H-phenalen-1-one (6), together with the four known compounds 7 -10. Their structures were elucidated by spectrometric methods including 1D-and 2D-NMR, and MS analysis. These compounds may be involved in allelopathic interactions of water hyacinth with neighboring plants.Introduction. -Water hyacinth (Eichhornia crassipes (Mart. ) Solms), a plant of the family Pontederiaceae, causes globally annual losses of more than $100 million to hydroelectricity generation, irrigation schemes, fisheries, riparian communities, and water transport [1]. The free-floating aquatic weed originating from the Amazon basin in South America has been introduced by man in China in the early 20th century [2]. However, water hyacinth possesses the ability to absorb heavy metals which accumulate in the root, making this plant of little use. Previous studies reported the isolation of some phenylphenalenes from water hyacinth [3 -5]. We collected the material of water hyacinth in Dianchi Lake at Kunming where the lake is severely polluted. Six new compounds, 2,3-dihydro-3,9-dihydroxy-5-methoxy-4-phenyl-1H-phenalen-1-one (1), 2,3-dihydro-8-methoxy-9-phenyl-1H-phenalene-1,4-diol (2), 2,3-dihydro-4,8-dimethoxy-9-phenyl-1H-phenalen-1-ol (3), 2,3-dihydro-9-(4-hydroxyphenyl)-8-methoxy-1H-phenalene-1,4-diol (4), 2,6-dimethoxy-9-phenyl-1H-phenalen-1-one (5), and 7-(4-hydroxyphenyl)-5,6-dimethoxy-1H-phenalen-1-one (6), together with four known ones, hydroxyanigorufone (¼ 2-hydroxy-9-(4-hydroxyphenyl)-1H-phenalen-1-one; 7) [3], 5,6-dimethoxy-7-phenyl-1H-phenalen-1-one (8) [4], 2-hydroxy-8-(4-hydroxyphenyl)-1H-phenalen-1-one (9) [5], and methyl ferulate (¼ methyl 3-(4-hydroxy-3-methoxyphenyl)prop-2-enoate; 10), were isolated from the whole plant of E. crassipes (Fig. 1). The known compounds have already been reported in this species.