The n-octanol/water partitioning coefficients (logKow) of three snlfonylurea herbicides, metsulfuron methyl, chlorsulfuron and bensulfuron methyl, and five of the degradation products were determined by the shake-flask method. The capacity factors (logK') were determined by RP-HPLC with ODS column and methanol-water eluent. Correlations between logKow and, logK' and molecular connectivity index were studied. Acute toxicity to the bacterium Photobacterium phosphoreum (15-min-logEC50) and the green alga Chlorella pyrenoidosa (96-h-logEC50) were determined and correhted with logKow and logK'. The quantitative structure-activity-relationship equations showed that logKow and logK' are linearly correhted with toxicity, and both logKow and logK' can be used in the prediction. No significant acute toxicity of the tested compounds to the chdocera Daphnia magna was observed in the laboratory tests, and this was explained by ionic forms of the compounds in neutral aqueous solution.