The molecular conformation and the microstructure of the slenderized wool fibers have been studied by the Raman spectroscopy. The typical bands analyzed in this paper include the amideⅠand amide Ⅲ regions, the C-C skeletal vibration region, and the S-S and C-S bond vibration regions. The experimental results show that ⅰ) the Raman spectroscopy can reveal the secondary structural transformation from α-helical to β-pleated sheet begin at the early stage of stretching; ⅱ) the stretching mechanism of wool fibers can be divided into two different mechanisms, I.e. The secondary structural transformation and the slippage of the polypeptide chain; and ⅲ) the stretching leads to the increasing of the amount of the disordered conformation and the decreasing of the amount of S-S bonds.