We developed several kinds of trial radiation-hardened MPPC models by changing structures; targeting future space applications for gamma-ray detectors. We produced two sample packages with 15 µ-type 1×1 mm2 MPPC elements for every 9 prototypes and then irradiated 150 MeV protons up to 10- and 100 krad for respective samples. We also used 15-, 25-, 50- and 100-µm-type MPPCs with the current design as controls. We evaluated the radiation tolerance mainly by increasing ratio of post-irradiation dark currents. Consequently we found that all trial models achieved significantly improved radiation tolerance peaking at a factor of 7−8 in the best case. We also present differences among control samples due to the various pixel sizes.