Two M79 grenades were fired at the head office of Siam Commercial Bank on Ratchadapisek Road late Wednesday night, police said.
The attack happened at 10:40 pm. The first grenade fell on the eight floor of the A Building, and the blast shattered glass windows.
The second bomb hit the ninth floor of the West 1 Building, which is an office of Unilever Thailand.
No one was injured.