R 2 Fe 3 Si 5 (R = Sc, Y, Lu) contains nonmagnetic iron and has a relatively high superconducting transition temperature T c among iron-containing superconductors. An anomalous temperature dependence of specific heat C(T) has been reported for polycrystalline samples down to 1 K. We have grown R 2 Fe 3 Si 5 single crystals, confirmed the anomalous C(T) dependence, and found a second drop in specific heat below 1 K. In Lu 2 Fe 3 Si 5 , we can reproduce C(T) below T c , assuming two distinct energy gaps 2 1 /k B T c = 4.4 and 2 2 /k B T c = 1.1, with nearly equal weights, indicating that Lu 2 Fe 3 Si 5 is a two-gap superconductor similar to MgB 2 . Hall coefficient measurements and band structure calculation also support the multiband contributions to the normal-state properties. The specific heat in the Sc 2 Fe 3 Si 5 single crystals also shows the two-gap feature. R 5 Ir 4 Si 10 (R = Sc, rare earth) is also a superconductor where competition between superconductivity and the charge-density wave is known for rare earths but not for Sc. We have performed detailed specific heat measurements on Sc 5 Ir 4 Si 10 single crystals and found that C(T) deviates slightly from the behavior expected for weak-coupling superconductors. C(T) for these superconductors can also be reproduced well by assuming two superconducting gaps.