A fiber optic 2-cholrophenol (2-CP) sensor was developed based on the fluorescence quenching of molecular oxygen on the oxygen-sensitive membrane and O2 consumption during catalytic oxidation reaction of 2-CP. The 2-CP concentration can be determined by utilizing a lock-in amplifier to measure the change in the fluorescence lifetime of an oxygen-sensitive membrane, in which the tris (2,2′-bipyridyl) ruthenium(II) chloride complexes (Ru(II)(byp)3Cl2) were immobilized in cellulose acetate (CA) via simple hybridized approach. The experimental results show the good linear relationship between the phase delay of sensitive membrane and 2-CP concentration in its detection range of 1×10-7 to 1×10-5 mol/L and 1×10-5 to 1×10-4 mol/L. The detection limit of the sensor is 7×10-8 mol/L (S/N=3) and the response time is 5 min. Our experimental measurements confirmed good response characteristics of the as-prepared fiber optic 2-CP sensor, as well as its capability to detect the 2-CP concentration in practical water samples.