We present the optical and spectroscopic characterization and the first example of laser operation of Yb doped LuYAG ceramics, with two different compositions, namely (Lu0.25Y0.75)3Al5O12 and (Lu0.50Y0.50)3Al5O12, both with 15% Yb doping. Ceramic samples were prepared by reactive sintering from high purity α-Al2O3, Lu2O3, Y2O3, Yb2O3 powders using Tetraethoxysilane (TEOS) and MgO as sintering aids. After ball milling, the slurry was dried, uniaxially pressed into 20 mm diameter pellets at 20 MPa, and then cold isostatically pressed at 200 MPa. Sintering was conducted at 1850°C for 30 h under vacuum, followed by annealing in air (1500 °C, 10 h) to remove the oxygen vacancies. Laser tests were carried out in a laser cavity end pumped by a fiber coupled diode laser emitting at 936 nm. A slope efficiency as high as 65.2% with a maximum output power of 8.7 W (in quasi-CW pumping conditions) was obtained from the sample with composition (Lu0.25Y0.75)3Al5O12, whereas the sample with composition (Lu0.50Y0.50)3Al5O12 had a maximum slope efficiency of 49.5% (due to the higher scattering losses), and 6.7 W of maximum output power. Furthermore we characterized the tuning range of the two samples.