An integrated optical single-channel add-drop multiplexer (SCADM) in SOI platform is proposed for fiber optic DWDM systems. The device (with two input ports & two output ports) is basically comprised of two single-mode waveguides (λ ~ 1550 nm). In course of their path (from their input ports), the two waveguides approach each other to form a directional coupler (3-dB power splitter), and apart away to form two arms of a Mach-Zehnder interferometer, come closure again to form another 3-dB power splitter, and finally separated to form two output ports. The incoming optical channels (separated by 200 GHz, ITU channel spacing, λ ~ 1550 nm) will be launched into one of the input ports. Any one channel in demand can be dropped at one of the output ports and the rest of the channels will be at the other output port. The other input port will be used to add another channel in demand.