Rubber composition for tire tread and pneumatic tire

A rubber composition for a tire tread comprising 100 parts by mass of a diene rubber, 10 to 150 parts by mass of a reinforcing filler, and 0.1 to 30 parts by mass of an acid-treated silk powder having a 90% volume particle diameter (D90) of 500 μm or less,

• wherein the acid-treated silk powder is a powder obtained by acid-treating a silk raw material without conducting an alkali treatment before said acid-treatment,
• wherein the acid-treated silk powder is a silk powder embrittled by an acid treatment, and has sericin on the surface thereof and fibroin inside the sericin, the content of sericin in the acid-treated silk powder is 30 to 15 mass %, and the content of fibroin in the acid-treated silk powder is 70 to 85 mass %,
• wherein the acid-treated silk powder is a silk powder obtained by applying a surface treatment for improving adhesiveness to a rubber to the acid-treated silk powder, and
• wherein the surface treatment for improving adhesiveness to a rubber is a surface treatment using an improving agent of adhesiveness comprising a resorcin-formalin resin precondensate and a latex.