An analytical method for the analysis of trace microcystins (MCYST) in water was developed using solid phase extraction (SPE) for enrichment and ultra performance liquid chromatography/tandem mass spectrometry (UPLC/MS/MS) for detection. One litre of water was passed through SPE columns, the extracted sample was rinsed off by 10 mL methanol, then evaporated to 1.0 mL before being analyzed with UPLC/MS/MS. The effect of formic acid concentration in the mobile phase on the sensitivity was studied and the results showed that 0.1% was the optimum concentration. Four microcystins, MCYST-LR, RR, LW, LF, can be separated and detected in 5 min, which is much shorter than that by the conventional liquid chromatography. The detection limits were 1.3 - 6.0 ng/L, and the recoveries were 91.1% - 111%. The calibration curves showed good linearity in the range of 1.0 microg/L - 1.0 mg/L with correlation coefficients larger than 0.99. The method was also applied to determine MCYST in real water samples from three reservoirs in Zhejiang Province, and the results showed that the concentrations of LR and RR were 0.044 7 - 2.73 microg/L and 0.020 8 - 1.36 microg/L respectively, and LW and LF were not detected.