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This paper shows that silk fibers produced by cecropia (Hyalophora cecropia) have similar tensile properties but different amino acid composition than that of mulberry (Bombyx mori) silk. The cecropia fibers are also much finer and have better strength and modulus than tasar silk, the most common non-mulberry silk. Cecropia is one of the largest silk producing moths and has similar lifecycle to that of mulberry silk but is easier to grow and produces larger cocoons than mulberry silk. In this study, we have characterized the composition, morphology, physical and tensile properties, and thermal behavior of the cecropia silk. Cecropia cocoons have a three tier structure and are larger (750 mg) than the cocoons produced by B. mori (650 mg). Fibers in the three layers in cecropia cocoons have tensile properties similar to that of B. mori silk but are finer (1.7–2 denier) and have higher strength (3.8–4.3 g/denier) and modulus (68–92 g/denier) than tasar silk.