Abstract: Risk mitigation is a hot topic in supply chain management. We consider a manufacturer faces an unreliable supplier with private information on high or low initial reliability, and the initial reliability can be enhanced through process improvement initiated by the manufacturer. By applying the principle-agent theory, the optimal contracts including both the manufacturer's process improvement and procurement decision are designed. By comparing the manufacturer's optimal contracts under full and asymmetric information, it is found that, information asymmetry decreases the probability that the manufacturer orders from the supplier with low initial reliability, and may lead to over-improvement on him. Information asymmetry does not necessarily decrease social welfare or lead to information rent. When the initial reliabilities and the supplier's Nash bargaining power satisfy some conditions, compared with the manufacturer's optimal procurement contracts, the Pareto improvement of the supply chain can be realized by the supplier's self-revelation of his private information. Numerical examples is used to verify the main conclusions. It is valuable and significant to the procurement activities under supply risk.

Key words: supply disruption, information asymmetry, process improvement, procurement contract