Continuous thermal and mechanical fatigue causes the generation of microcracks in structural polymer materials. The cracks reduce the mechanical strength of the materials, eventually resulting in their collapse. Because cracking occurs deep within the materials, the damage is difficult to detect and manually repair. To heal the cracks automatically, a new system has been reported in which microcapsules containing a healing agent are incorporated into polymer materials. Cracks rupture the microcapsules, releasing a high content of healing agent and resulting in efficient healing of cracks. In this study, we report a model for healing at low temperature by using a metal catalyst. A reactive monomer was encapsulated as a healing agent in melamine formaldehyde microcapsules prepared by in-situ polymerization. Cobalt bromide was added as a catalyst, and a model material with microcapsules and catalyst was found to heal up to 75% of cracks at 60 degrees C compared to the original material without microcapsules and catalyst. When up to 15 wt% of microcapsules was incorporated into the polymer material, the flexural modulus of the material was maintained at 3.0 GPa.