A first epoxy resin composition is described that includes [A] at least one epoxy resin, [B] at least two hardeners comprising [B-1] at least a first hardener and [B-2] at least a second hardener different from the first hardener, and [C] at least one accelerator, wherein the epoxy resin composition satisfies 5.0>|T1−T2|, where [A], [B], [C], T1 and T2 are as defined. A second epoxy resin composition is described that includes [A] at least one epoxy resin, [B] at least two hardeners comprising [B-1] at least one amine compound and [B-2] at least one organic acid hydrazide compound, and [C] at least one accelerator comprising [C-1] at least one organophosphorus compound, where [A], [B] and [C-1] are as defined. A prepreg comprising reinforcing fiber bundles impregnated with the first epoxy resin or the second epoxy resin is also described as well as a fiber-reinforced composite material.