Nutrients are routine aspects for marine environment monitoring. With low concentration in oceans, nutrients are difficult to be measured with a routine spectrophotometer. Based on liquid core waveguides, a new high-sensitivity analyzer was constructed to measure trace nutrients in oceans. The analyzer can provide continuous measurement of spectral absorbance of water sample in the spectral range from 350 to 900 nm with a spectral resolution of 1.02 nm. The processes such as sample injection, data acquisition of absorbance and data analysis are automatically controlled by a built-in PC104 micro computer. The results of test proved that, with the reaction time of about three minutes, the analyzer could provide a detection limit of the order of nmol x L(-1), which is about 1 000 times lower than that of routine spectrophotometer. The analyzer is amenable to trace nutrients monitoring in oceans.