The elasticity of spider MAA silks containing varying proline content was investigated and compared with that of silkworm ( Bombyx mori) silk. For silks with similar breaking strain (suggesting similar molecular order), the elasticity appears to increase with increasing proline content. Particularly, across all spider silks, intra- and interspecies relationships are found between capacity to shrink (Csh) and strain recovery, while only the interspecies relationship is found between Csh and work recovery. Four factors, that is, molecular orientation, crystallinity, amino acid motif, and hydration, are discussed to explain the origin of silk's elasticity. Our study corroborates the view that proline-containing motifs contribute to the elasticity of not only spider silks, but also other bioelastomers.