A passively mode-locked fiber ring cavity laser with a small segment of Er3+/Yb3+co-doped fiber as gain medium, pumped by stable 976 nm laser diode and mode-locked by the nonlinear polarization rotation technique, experimentally demonstrated. By adjusting the polarization controllers orientation and pump power, the stable operations of continual fundamental wave mode-locked with the repetition rate of 15.90 MHz and the spectral bandwidth of 7.4 nm, Q-switched-mode-locked with the spectral bandwidth of 4.84 nm, passive Q-switched with the repetition rate of 147.06 kHz and the spectral bandwidth of 1.8 nm, high-order harmonically mode-locked regimes in a ring cavity Er3+/Yb3+co-doped fiber laser have been obtained experimentally. Compared with Er3+ fiber as gain medium, the experiment accomplished by using Er3+/Yb3+co-doped fiber as gain medium shows a better output of mode-locking.