Abstract: Experiment of the double-clad Yb-doped fiber amplifiers is discussed. The signal with 7 mW average power at 25.4 MHz repetition rate is amplified to 505 mW by using 0.5 m length of double-clad Yb-doped fiber when launched pumping power is 1.9 W, corresponding to a pulse energy of 19.8 nJ. The width of the pulses is compressed to about 2.7 ps by grating pair compressor.