According to the present invention, there are provided lithium titanate particles which exhibit an excellent initial discharge capacity and an enhanced high-efficiency discharge capacity retention rate as an active substance for non-aqueous electrolyte secondary batteries and a process for producing the lithium titanate particles, and Mg-containing lithium titanate particles. The present invention relates to lithium titanate particles with a spinel structure comprising TiO 2 in an amount of not more than 1.5%, Li 2 TiO 3 in an amount of not less than 1% and not more than 6%, and Li 4 Ti 5 O 12 in an amount of not less than 94% and not more than 99% as determined according to Rietveld analysis when indexed with Fd-3m by XRD, and having a specific surface area of 7 to 15 m 2 /g as measured by BET method, a process for producing lithium titanate particles comprising the steps of adding and mixing a water-soluble lithium solution into a water suspension of an oxide of titanium having a BET specific surface area of 40 to 400 m 2 /g and a primary particle diameter of 5 to 50 nm and subjecting the resulting mixed suspension to aging reaction at a temperature of 50 to 100°C; subjecting the resulting reaction product to filtration, drying and pulverization; and subjecting the obtained dry particles to heat-calcination treatment at a temperature of 550 to 800°C, and Mg-containing lithium titanate particles having a composition represented by the formula: Li x Mg y Ti z O 4 wherein x, z > 0; 0.01 ‰¤ y ‰¤ 0.20; 0.01 ‰¤ y/z ‰¤ 0.10; and 0.5 ‰¤ (x + y)/z ‰¤ 1.0, the Mg-containing lithium titanate particles having a BET specific surface area of 5 to 50 m 2 /g, a spinel single phase as a crystal structure, and a lattice constant (a) represented by a value of 0.050y + 8.3595 < a ‰¤ 0.080y + 8.3595 (Å).