To improve fracture toughness and encourage excellent self-crack-healing ability, mullite/SiC particle/SiC whisker multi-composites and mullite/SiC whisker composites were hot pressed. The crack-healing abilities and mechanical properties of these sintered composites were investigated. Based on the obtained results, the usefulness of the mullite composite as a material for springs was discussed. The part of mullite/15 vol% SiC whisker/SiC 10 vol% particle containing healed cracks retained high reliability over the whole measured temperature range. When the crack-healing ability was endowed by SiC whiskers alone, the parts containing the healed pre-cracks were found to have a heat-resistance limit temperature. Mullite/15 vol% SiC whisker/10 vol% SiC particle multi-composite had the best potential as a material for springs used at high temperatures, because it had an adequate crack-healing ability as well as shear deformation ability almost two times stronger than that of monolithic mullite.