A waveguide laser in an ytterbium-doped tantalum pentoxide film is reported. The waveguide is formed of a rib of sputtered tantalum pentoxide on top of oxidized silicon with an over-cladding of silica. Emission at a wavelength of 1025 nm was achieved with an absorbed pump power threshold and slope efficiency of ≈29 mW and 27%, respectively, for a cavity formed by a high reflector mirror and an estimated 12% Fresnel reflection from the bare end-face at the output.