Smart metering systems provide high resolution, realtime end user power consumption data for utilities to better monitor and control the system, and for end users to better manage their energy usage and bills. However, the high resolution realtime power consumption data can also be used to extract end user activity details, which could pose a great threat to user privacy. In this work, we propose a secure multi-party computation (SMC) based privacy preserving protocol for smart meter based load management. Using SMC and a proper designed electricity plan, the utility is able to perform real time demand management with individual users, without knowing the actual value of each user's consumption data. Using homomorphic encryption, the billing is secure and verifiable. We have further implemented a demonstration system which includes a graphical user interface and simulates network communication. The demonstration shows that the proposed privacy preserving protocol is feasible for implementation on commodity IT systems.