Amyloid fibrils are associated with various degenerative diseases ranging from Alzheimer's diseases, Parkinson's diseases, prion diseases to type-II diabetes and immunoglobulin light chain associated amyloidosis. The molecular mechanism of amyloid fibril formation is not only informative for developing therapeutic strategies against the diseases, but also interesting for the study of protein folding problems. Various proteins are found to be able to form amyloid fibril in vitro under certain physical conditions. We chose hen egg white lysozyme for our study because its structure has been studied extensively and it is known to form amyloid fibrils in vitro under appropriate conditions. The inhomogeneity of the system complicates the application of many conventional biophysical techniques. A home-built deep UV resonance Raman apparatus with a tunable laser source (193-205 nm) is used for characterizing amyloid fibril formation. The Raman scattering of amide chromophore, the building block of polypeptide chain, and aromatic side chains of phenylalanine and tyrosine are resonantly enhanced. The amide vibrational modes provide information about the secondary structural transformation. Phenylalanine was used as a natural deep UV Raman spectroscopic biomarker for characterizing tertiary structural changes. High quality Raman spectra were obtained for lysozyme at all stages of fibril formation. An irreversible unfolding was characterized as the first stage of fibril formation. The irreversible unfolding was also characterized to be an all-or-none transition, which means that the native lysozyme unfolds into a partially unfolded intermediate, which then assemble into the fibril.