Abstract: Design of a multiplexer is a complicated task in modern automatic measurement and control systems, especially for sampling of low level signals on the spot. A complementary MOS-lightcoupled multiplexer is presented, in which complementary MOS analog gates drawn out from the substrate with a wire are used as switch components, lightcoupleddevices drawn out from two ends with wires - as isolate-shieldedcomponents and integrated gates- as control components. Its test is asuccess.The advantages of the multiplexer are summarized as follows:1.Its isolate-shielded performance is quite desirable, and it is capable of three line sampling and application in the spots with strong interference.2.The influence of grid leakage currents and peak interference can be eliminated. As its noise is about ±1μv, it can deal with low level signals.3.In a wide measurement range its ON-resistance is low and only 10 to 30 ohms when the input level is between +3 to - 3 volts.4.Its turn-on time is short, in the level of microseconds.5.It can be driven by TTL integrated gate and easy of further integration.