A general method for preparing mechanically strong hydrogels that can undergo light-triggered healing was demonstrated. By loading a small amount of gold nanoparticles (AuNPs, 0.05 wt%) in hydrogels prepared with stearyl acrylate (SA), N,N-dimethylacrylamide (DMA) and N,N′-methylenebisacrylamide (MBA), whose strength is endowed by chemical crosslinking coexisting with crystallized hydrophobic SA side chains acting as the physical crosslinks, exposing a cut-through damage to a laser of wavelength at the surface plasmon resonance of AuNPs and subsequently turning off the light, gives rise to efficient healing of the hydrogel as a result of the reversible melting–crystallization phase transition of the hydrophobically associated SA chains. A hydrogel of this kind exhibits an unprecedented tensile strength, after repairing, of greater than 2 MPa. It also displays a light-controllable shape memory effect.