The 34 layers tapCuPo, the copper tera-4- ( 2.4-ditert-ampylphenoxy) phtha-locyanine, were deposited by the LB technique on the optical glass waveguide of K+ ion-exchange, and a four-layer dielectric waveguide with LB films cladding is formed. The 532 nm line from a YAG laser is used as a light source. The input light with pulse width of 250 ps is coupled into the optical waveguide by a glass prism, and then is passed through the regiod coated with the LB films. In the experiment,a fast optical bistability with the switching off time to 24 ps has been demonstrated.