A fast, simple and sensitive method for the determination of cyanobacterial hepatotoxin, microcystin-LR (MC-LR) , was developed using solid phase microextraction coupled to high performance liquid chromatography (SPME-HPLC). Extraction and desorption conditions, such as pH and ionic strength of the sample medium as well as sampling and desorption duration, of the SPME process were optimized. Partition coefficient for the distribution of MC-LR between the PDMS/DVB-SPME stationary phase and the aqueous phase was estimated to be 5.4+ 0.18 x 103. Relative repeatability of 6.4% (n=10, P>0.05) and detection limit of 10 ng/ml (n=8, P>0.05) were achieved.