We report on an acousto-optic Q-switched 1645 nm Er:YAG ceramic laser resonantly pumped by using an Er,Yb fiber laser at 1532 nm. Maximum continuous wave output powers of 2.1 W and 2.4 W were obtained for 10% and 20% transmission OCs under 10.5 W of incident pump power, respectively. In Q-switched mode, the laser produced pulses with ~3.7 mJ energy and 82 ns width at 200 Hz repetition rate for 20% transmission OC under 8.6 W of incident pump power, corresponding to a peak power of ~45 kW.