By applying an optimized chelate gas phase deposition technique, a Yb/Ce codoped aluminosilicate fiber with ultra-low loss of 1.55 dB/km was successfully fabricated and reported. The fiber showed homogenous distribution of the refractive index and dopant concentration devoid of central dip and clustering. Using the fiber as the amplifier stage, it delivered 1023 W near-single-mode laser output (M2=1.35) with a high slope efficiency of 85.1%, and the fiber temperature was less than 24.2°C, primarily benefiting from the ultra-low background loss. The fiber also exhibited low photodarkening-induced loss, illustrating its outstanding photodarkening resistance. These results indicate that the ultra-low-loss Yb/Ce codoped aluminosilicate fiber is a prospective candidate for stable and reliable fiber laser applications.