Tire rubber composition and pneumatic tire

The invention aims to provide a tire rubber composition that is excellent in the low heat build-up property (fuel economy), wet grip performance, and abrasion resistance, and can be suitably used for a tread (cap tread); and a tire rubber composition that is excellent in the low heat build-up property and breaking properties, and can be suitably used for a base tread or sidewall. The composition comprises: a diene polymer; and silica, the diene polymer being a modified diene polymer obtainable by reacting compounds (A) and (B), the compound (A) being an active alkali metal-terminated conjugated diene polymer obtainable by polymerizing a conjugated diene monomer alone or with an aromatic vinyl monomer, in the presence of compound (C), the compound (B) being a modifying agent having a functional group, and the compound (C) being a chemical species obtainable by reacting an organic alkali metal compound with compound of formula (1):