Advanced lithium orthosilicate (Li 4 SiO 4 ) pebbles with additions of lithium metatitanate (Li 2 TiO 3 ) as a secondary phase have attracted international attention as an alternative solid-state candidate for the tritium breeding in future nuclear fusion reactors. In this research, the generation of radiation-induced defects in the Li 4 SiO 4 pebbles with various contents of Li 2 TiO 3 was analysed in-situ by X-ray induced luminescence technique. After irradiation with X-rays, the accumulated radiation-induced defects in the Li 4 SiO 4 pebbles were studied by electron spin resonance, thermally stimulated luminescence and absorption spectrometry. On the basis of the obtained results, it is concluded that the generation mechanism and the structure of primary radiation-induced defects (except Ti 3+ centres) in the advanced Li 4 SiO 4 pebbles with additions of Li 2 TiO 3 under exposure to X-rays is similar to the single-phase ceramics. In addition, it is expected that the additions of Li 2 TiO 3 can increase the probability for the recombination processes of primary radiation-induced defects in the advanced Li 4 SiO 4 pebbles during irradiation and thereby reduce the formation of thermally stable radiolysis products, such as colloidal lithium particles.