For safety reasons, it is desirable to measure radiation as remotely as possible. For remote measurement of gamma radiation, the fiber-optic sensor (FOS) was developed in this study by combining a plastic optical fiber and an inorganic scintillator. To identify the best shape of the sensing probe of the FOS in terms of its detection efficiency, three different shapes of probe were fabricated using an inorganic scintillator: a cylinder and two bundles of different lengths (30 and 10 mm). To identify the best reflector for the sensing probe, the side of each probe was wrapped with one of three different reflectors: Teflon tape, TYVEK 1056D, and aluminum foil. In this study, a total of twelve different sensing probes were prepared: three different shapes of sensing probes with three different reflectors, and three different shapes of the sensing probes without reflectors. To measure gamma radiation, a cesium-137 source (1 μCi) in a disk shape, 26 mm in diameter, was attached to the end of the sensing probes. The measurements showed that bundle shape II (a bundle of 26 inorganic scintialltors, 1 mm in diameter and 10 mm in length) was the best shape for the sensing probe, and aluminum foil was the best reflector.