Recently, more attention is given to HumanComputer Interaction (HCI) systems, which aim at making computer technology more usable for people by recognizing their affective states. Pupil diameter (PD) has been addressed as the most reliable approach for it is controlled by Automatic Nervous System (ANS) and is easy to detect. The goal of this paper is to identify the effect of gender on individual's emotional states. The paper introduces experimental results obtained using eye-tracking system with 30 participants. It starts by describing emotion recognition and its applications. Then, it describes the experiment procedure, stimuli and dataset used and discusses the findings. Finally, some Challenging issues are outlined. © 2013 IEEE.