Attenuated total reflection-Fourier transform infrared (ATR-FTIR) spectroscopy was applied to sericin fiber spun by Sericin-hope silkworms, developed to produce silk protein sericin in large amounts, and to a native sericin solution before spinning. Polarized ATR-FTIR measurement showed little orientation of sericin molecules in sericin fiber. Secondary structures of sericin fiber and native sericin were analyzed by Fourier self-deconvolution and curve fitting. The drying process of the native sericin solution was also followed to determine the effect of dehydration on sericin conformation. These analyses showed that β-sheets in native sericin increased with drying and that the secondary structure of air-dried sericin was similar to that of sericin fiber. These observations suggest that drying is a significant factor in the structural transition of sericin during fiber formation and that sericin undergoes only modest structural changes by spinning compared with fibroin.