A stable continuous-wave mode-locked picosecond Yb:LSO laser was demonstrated. The 5% doped Yb3+Lu2SiO5 (Yb:LSO) crystal was used as the laser medium, and a semiconductor saturable absorber was employed to realize mode-locking. With the pump power of 2 W, the output picosecond pulse power is 70 mW, at the repetition rate of 69.8 MHz. The measured pulse width is 3.6 ps, and the center wavelength can be at 1047 nm or 1066 nm.