Exploiting Tm-Ho codoped fiber as the saturable absorber, stable passive Q-switching and mode-locking of an Er-doped fiber ring laser is achieved. In the Q-switching operation mode, the repetition rate is tunable with pump power from several kHz to tens of kHz at 1567.8 nm, and the pulse duration is at the μs level. With polarization control, Q-switched mode-locking operation is observed at 1535.2 nm. Further increasing the pump power and tuning the polarization controller, mode-locking is achieved with repetition rate of tens of MHz and pulse duration of tens of ns. With even higher pump power, 2nd order rational harmonic mode locking is obtained. The experiments demonstrate that Tm-Ho codoped fiber is an excellent saturable absorber for all fiber passive Q-switching and mode-locking of Er-doped fiber lasers.