Commercial linear alkylbenzene sulfonate (LAS), mixture of alkylchain lengths and phenyl position isomers (C10-C13), is widely used as a major constituent of household and industrial detergents in the People’s Republic of China. Degradation process and behaviour of LAS compounds during an 82-hour lake water die-away study, with an added LAS concentration of 1. 5mg .L-1, was quantified and accomplished by HPLO-UV after extractionon the SepPek C18 reversed - phase cartridges. The degradation rate became progressively faster with increasing chain length. The technique described in this study is fast, sensitive and specific, and can be used to determine low levels, of LAS and for establishing water quality criteria and standards relating to LAS and its compounds. Commercial linear alkylbenzene sulfonate (LAS), mixture of alkyl chain lengths and phenyl position isomers (C10-C13), is widely used as a major constituent of households and industrial detergents in the People’s Republic of China. Degradation process and behavior of LAS compounds during an 82-hour lake water die-away study, with an added LAS concentration of 1.5 mg. L-1, was quantified and accomplished by HPLO-UV after extraction on the SepPek C18 reversed-phase cartridges. The degradation rate became progressively faster with increasing chain length. The technique described in this study is fast, sensitive and specific, and can be used to determine low levels, of LAS and for establishing water quality criteria and standards relating to LAS and its compounds.