Evacuee behaviors have significant influence on the efficiency of emergency evacuation in buildings. While crowd evacuee behaviors have been extensively examined with various simulation models, the understanding of individual evacuee behaviors has to date mostly relied on sociological models, which are usually subjective and descriptive. Using latest advances in virtual reality (VR) technologies, it is possible to create immersive virtual environments (IVEs) that can be used for behavioral experiments in controlled setups to examine individual evacuee behaviors. One challenge in conducting such experiments is to ensure their ecological validity, so that the decisions and actions made by the experiment subjects are what they would actually make in reality. As a first step to achieve sufficient ecological validity, this study examines the feasibility of using a combination of subjective and objective measures, including an emotion scale and a physiological indicator, to assess the emotional responses of subjects in IVE-based evacuation experiments. Two IVEs were developed in this study, both representing a fire emergency scenario in an apartment but having different levels of realism and hence different levels of ecological validity. Subjects were asked to perform an evacuation task in both IVEs, and their emotional responses were monitored and analyzed throughout the experiments. Statistical difference was observed between the subjects? emotional responses when exposed to the two IVEs. The results suggested it was feasible to assess the ecological validity by assessing the emotional response of the subjects in IVE-based evacuation experiments.