Abstract: Clock recovery and decision circuit applied to optical fiber communication is investigated. GaAs decision circuit and clock recovery circuit fabricated with depletion-mode GaAs metal-semiconductor field-effect transistors (MESFET's) has been designed. The base circuit cell of the decision circuit is source-coupled field-effect transistor logic (SCFL) circuit. The clock recovery circuit contains a preprocessor and a phase-locked loop (PLL). It is proved by simulation analysis that the clock recovery circuit can recover 2.5 GHz clock signal from the input and the 2.5 Gbit/s decision circuit can deal with input signal rightly and produce correct digital output signal after being sampled by recovered clock. It is proved by test that the 2.5 Gbit/s circuit can deal with input signal and produce output signal rightly after being sampled by recovered clock.