A fluorophore of 1,4 bis(1,3 benzoxazol 2 yl)benzene(BBOB) was selected as sensing molecule for constructing a new metronidazole
optic fiber sensor. The sensing performence is based on the fluorescence quenching of the plasticized PVC optode membrane trapped with BBOB by metronidazole. The quenching mechanism includes a primary inner filter effect and the formation of a charge transfer complex between BBOB and metronidazole extracted from aqueous phase into membrane phase. In the range of 4.00×10 -6 ￣1.00×10 -4 mol/L, the sensor responds linearly to metronidazole with a detection limit of 1.0×10 -6 mol/L metronidazole. A good reversibility and a rapid response within 30 s were obtained. The relative standard deviation of repeating measurements of 1.00×10 -4 mol/L metronidazole is 0.82%( n =10). The sensor shows good selectivity over the common inorganic ions and pharmaceutical species and therefore can be used for the direct determination of metronidazole in commercial preparations, the results were in agreement with those obtained by pharmacopoeia method.