In this paper, the all-optical switching polymer composites based on poly( methyl methacrylate) (PMMA) and azobenzene dyes were prepared. The optical switching effects of the composites were measured by using 514 nm pump beam and 632.8 nm probe beam. The composites' photoinduced reversible and repeatable change in the transmittance of the probe beam is attributed to the photoisomerization of the azobenzene dyes. The influencing factors of the optical switching properties, such as the modulation frequency, pump beam intensity and temperature, were studied experimentally. The effects of pump beam power and temperature on the optical switching response were also studied experimentally. (C) 2003 Kluwer Academic Publishers.