Disclosed is a hydraulic circuit for controlling booms of construction equipment, wherein working oil which is relieved from a large chamber of a boom cylinder passes through an orifice so as to prevent the boom from lowering if an overload is applied when the boom is not being operated. The hydraulic circuit for controlling booms of construction equipment includes: a boom cylinder which is connected to a hydraulic pump via a first path and a second path; a boom control valve which is mounted on the path between the hydraulic pump and the boom cylinder; a holding valve which is mounted between the boom control valve and the first path of the boom cylinder and prevents the natural lowering of a boom when the boom control valve is in a neutral position; a port relief valve which is mounted to the first path at the lower side of a holding poppet and relieves working oil when an overload is generated at the first path; and an orifice valve which is mounted at the lower side of the port relief valve, relieves the
