A new optical oxygen sensor based on the luminescence intensities of thenoyltrifluaroacetonato 1,10-phenanthroline europium (III) complex (Eu(TTA)(3)phen) immobilized in poly(styrene-co-trifluoroethylmethacrylate) film was developed. The luminescence intensity of the Eu(TTA)(3)phen film decreased with increasing the oxygen concentration. A Stern-Volmer plot of the Eu(TTA)(3)phen film exhibited considerable linearity (r(2) = 0.996) and the Stern-Volmer quenching constant, K-SV is estimated to be 0.015 %(-1).