Energy system is undergoing remarkable changes due to many factors including increase use of renewables, environmental consideration and technological advancements. This demands for new tools and methods for its efficient and smooth operation. This work proposes distributed demand response application using Multi-Agent System (MAS) for improving voltage in distribution network at port city. Contract-Net-Protocol (CNP) based scheme was used for communication and coordination between agents. A co-simulation framework including power system simulator and agent environment was used to evaluate the proposed MAS based approach. A test network including variable and intermittent renewable generation sources (wind, pv), flexible loads (reefers), non-flexible loads was used to investigate the MAS based approach. Results show that MAS based approach is quite effective for demand response application.