Optically reconfigurable gate arrays (ORGAs) have been developed to realize radiation-hardened field programmable gate arrays (FPGAs). An ORGA consists of a laser array, a holographic memory, and a programmable gate array VLSI. Since the configuration of an ORGA is a parallel configuration, damage to a configuration circuit or a component does not affect configuration procedures on other configuration circuits. Therefore, even if almost all look-up tables (LUTs) malfunction because of radiation, the remaining functional LUTs can be programmed and used, whereas the serial configuration of FPGAs does not allow the use of a partly failed gate array. However, to achieve higher radiation tolerance of a programmable gate array than that of an FPGA in ORGA architecture, the radiation tolerances of a laser array and a holographic memory must be sufficiently higher than that of the part of a programmable gate array VLSI. Since the radiation tolerance of a holographic memory has already been confirmed as sufficiently higher than that of a programmable gate array VLSI, this paper presents a radiation tolerance investigation of a laser array on an optically reconfigurable gate array. Experiments using Co60 gamma radiation have demonstrated that a laser array has a greater than 20 Mrad total ionizing dose tolerance.