Advances in computer-based information technology in recent years have led to a wide variety of decision support systems (DSS) that managers or decision makers are now using to make and implement decisions. The difference between success and failure is the extent to which managers can use the system to increase their effectiveness with their organization. Thus, any system viewed as a successful system must have some impact on a decision maker's behavior. Although DSSs are designed to support decision makers in varied situations, empirically there is little evidence about how satisfactory they are in practice. To make DSS more effective and efficient, first, analysts should know decision making activities well. Then they are able to focus on improving adaptability of DSSs. The decision making activity contains the decision making cycle, decision makers' behavior, how DSSs affect decision making activitYJ and how DSSs help decision makers achieve better decision output. The objective of this research is to observe the influence of a DSS on decision makers' behavior through a simulation experiment involving scheduling and dispatching decision making. The experimental result showed that human decision making is superior to typical dispatching rules. To some extent, decision makers believed DSS change decision output, decision process and their concept of decision situations. In addition, the result revealed that DSS is more likely to be useful in solving complex problems, and decision makers with DSS are overall more efficient than those without DSS.