Abstract Lithium ceramic spheres have been proposed as a tritium breeding material for a fusion reactor blanket. Spheres fabricated by Schott, Mainz show a glass-like structure in light and scanning electron microscopy. A crystalline structure, however, was detected by X-ray diffraction. Part of the spheres were annealed at 1000°C for 2 h to heal microcracks and to relieve internal stress. After annealing a grain structure was found by microscopy with grains of 10–30 μm grain size. When stored in air the spheres took up moisture. After some days the water content yielded 2–3 mol%. A thermo-mechanical test was conducted with the spheres by cycling between 60 and 600°C in a stainless steel capsule which simulated the pressure load during thermal cycling of the fusion reactor blanket. Examination of the spheres after 10 cycles showed that 11% of as-fabricated spheres were broken. The amount of broken spheres which had been annealed was only 2%. It is assumed that healing of microcracks and relieve of internal stress improves the behavior of the spheres.