A novel micro flow injection analysis system was developed for the potentiometric determination of tetraborate ions in environmental samples. The flow system was created by embedding the previously developed tetraborate selective sensor into a home-made micro-flow cell with dead volume. The flow conditions of the system was optimized. The potentiometric performance of the tetraborate selective sensor was characterized using the optimized flow conditions. The sensor showed a supra-Nernstian slope of 45.7 +/- 1.3 mV/decade of activity in the tetraborate concentration range from 1.0 x 10(-4)to 1.0 x 10(-1 )mol L(-1)with a correlation coefficient equal to 0.9994. The detection limit of the tetraborate sensor was observed to be 9.6 x 10(-5 )mol L-1. The sensor exhibited a rapid response time, good selectivity, and favorable repeatability toward tetraborate ions. Additionally, the selective tetraborate sensor displayed good operational stability and its average lifetime was determined to be 14 weeks in the flow injection analysis system. The sensor was also successfully applied for the direct potentiometric determination of tetraborate ions in environmental samples using the optimized micro flow injection analysis system.