In this paper we present the crystal growth and optical characterization of thulium-doped KYb(WO4)2 ~hereafter KYbW!. We grew thulium-doped KYbW monoclinic single crystals with optimal crystalline quality by the top-seeded-solution-growth ~TSSG! slow-cooling method. Thulium spectroscopy was characterized in this host. The Judd-Ofelt parameters determined were V250.14310220 cm2, V450.21310220 cm2, and V650.10310220 cm2. The room temperature lifetimes measured for KYbW:Tm 1% were t(1G4) 560–70 ms, t(3H4)590 ms and t(3F4)5200 ms. We calculated the emission cross section for several channels. There was an important blue emission after pumping resonantly to the stoichiometric ytterbium at 980 nm, and we studied the emission channels of thulium. The presence of thulium luminescence is proof of the large transfer of energy in this compound.