Environmental problems are recognized as one of the most serious issues in these last few decades. Green supply chain management and sustainable supply chain management have gained increasing attention within both academia and industry. Previous studies proposed a closed-loop supply chain model and a negotiation protocol for increasing the amount of reused products and reducing waste products. This study improves the negotiation protocol for further increasing the reused products and reducing the waste. A remanufacturer can economically collect a lot of used products by negotiating with a client in consideration of both the required prices from the remanufacture and the possible times to dispose of the used products from the client. A prototype of a simulation system for a closed-loop supply chain is developed in order to evaluate the effectiveness of the new negotiation protocol. Experimental results show that the new protocol can reuse more products than the previous one.