Protein folding study has become a very active research field in recent years. The molten globule (MG) state, which has extensive secondary structure but lacks compact tertiary structure, has been proposed to be an intermediate on the protein folding pathway and has been studied widely. The aim of this research is to characterize the structure of some MG like states as well as other non-native states of proteins and study their roles on the protein folding/unfolding pathway. Several optical spectroscopic tools including circular dichroism (CD, both in UV and IR region), FTIR, UV-Vis and fluorescence were applied to characterize protein structures as steady states. Meanwhile, stopped-flow CD, fluorescence and FTIR were used to monitor the kinetic changes. Cytochrome c (cyt c) has various conformations under different conditions, which were differentiated by the complementary information obtained from several optical spectroscopic methods. Sodium dodecyl sulfate (SDS), an ionic surfactant, was shown to refold acid denatured cyt c resulting in a MG-like state at both submicellar and micellar concentrations. The structural model for this protein-surfactant complex was then discussed. Time-resolved experiments were carried out to study the effect of salt and SDS on the refolding of acid denatured cyt c. Results suggest that the salt-induced MG state may not exist on the refolding pathway of acid denatured state to native state, while SDS-induced refolding shows different behaviors at submicellar and micellar concentrations. Non-native states of concanavalin A were obtained by the effect of TFE, inducing a β-sheet → α-helix transition. The α-helical structure was characterized by various optical spectroscopic tools, and its stability depends on conditions such as protein concentration and pH. Slow transition of α-helix to an aggregated form can be observed under certain pH conditions at high protein concentration. The fast protein unfolding (β → α) process was monitored using stopped-flow CD and fluorescence, and a homemade stopped-flow FTIR system was used to monitor both the fast and slow transitions. Unfolding mechanisms were then proposed based on these kinetic results.