The consumers' quality consciousness and manufacturer' s process innovation ability in a supply chain have an impact on the level of quality choice． Taking this into account，this paper investigates the optimal decisions-making on both quality and quantity in a centralized and a two-stage decentralized supply chain， respectively． The decentralized supply chain consists of a manufacturer and a retailer; the former is an optimization problem and the latter is a Stackelberg game in which the manufacturer is the leader and the retailer is the follower． These two problems above are modeled，and closed-form solutions are obtained． The paper also examines the impacts of the parameters of quality cost，consumers' quality consciousness and manufacturer' s process innovation ability on supply chain decisions， supply chain profits and consumers'surplus． Also，a computational study is used to explore the sensitivities of the optimal decisions，profits and consumers'surplus in the decentralized supply chain to the consumers'quality consciousness and manufacturer's process innovation ability． It is found that the higher the consumers' quality consciousness or the stronger the manufacturer' s process innovation ability is，the higher the quality and quantity are in the supply chain; the high-quality， high-yield policy brings to the supply chain more profits and the consumers' surplus can also be improved． Further， social welfare increases and the resources are effectively utilized． In addition，the double marginalization effect is not always dominant in the distribution channel in view of the impact of channel selection on both the consumer's quality consciousness and manufacturer's process innovation ability． This kind of double marginalization effect will diminish or even disappear as the consumer's quality consciousness and manufacturer'sprocess innovation ability increase in the distribution channel． This study also shows some management insights into the public sector's ( such as government) guidance and supervision of quality problems．