Nanoparticle chain aggregates (NCA) possess elastomeric properties including stretch under tension, and contraction when the tension is relaxed. Individual chain aggregates of 7 nm titania particles a few hundred nm long were observed in the electron microscope. The NCA were stretched across expanding holes in the carbon film on an electron micrograph grid. After stretching up to 90%, the NCA broke loose at one end and contracted to a tightly folded chain. This pattern was observed in repeated tests. Mechanisms for this behavior and reasons for its generality are proposed. Implications are discussed for the ductility of nanoparticle ceramics, and the increased tensile strength and elastic modulus of rubber due to nanoparticle additives. © 1998 American Institute of Physics.