Humans' ability to discriminate a Duchenne (genuine) smile from non-Duchenne (“presented”) smile attracted scientific interests among various types of smiles. To better understand humans' capability and its mechanisms to discriminate Duchenne and non-Duchenne smiles, we examined people's observational behaviors during Duchenne/non-Duchenne discrimination tasks using an eye-tracker. In so doing, we also collected data on participants' personality traits as some previous studies showed that observational behaviors are strongly influenced by the personality traits of observers. With two Experiment, we found differences in observational behaviors between correct and incorrect discrimination, and that different personality traits were associated with different observational behaviors. However, we did not found any significant relationship between observers' personality traits and judgment accuracies. Thus, although we found differential observational behaviors for correct and incorrect respondents, it seems that these differences were nothing to do with participants' personality traits.