The diffusion of oxygen into pyrene labelled polystyrene (PS) latex/poly(N-isopropylacrylamide) (PNIPAM) composite films (PS/PNIPAM) was studied based on PS content with the use of fluorescence quenching method. Fluorescence experiments were carried out on composite films containing pyrene as a sensor dye. The Stern-Volmer equation for fluorescence quenching is combined with Fick's law for diffusion to derive mathematical expressions. Diffusion coefficients (D) were produced and found to be decreased with increasing PS content. This decrease was explained with the formation of a tortuous path for diffusing gas molecules, which extends the diffusion path of oxygen in the films. In addition, at high PS content, two different D values were obtained, which were attributed to the existence of two different areas in the composite films.