The present research aimed to investigate the relationship between psychological wellbeing, optimism and existential anxiety in elderly men. Therefore, the research employs a descriptive and correlational method. The statistical population included all the elderly m en spending time at the parks of Karaj City. Our sample comprised 200 individuals who were randomly selected and responded to the anonymous questionnaires. The data gathering tools included Psychological Wellbeing Questionnaire, Optimism Questionnaire and Existential Anxiety Questionnaire. The findings indicate significant and negative relationship between psychological wellbeing and existential anxiety. This is to say that, with the increase of psychological wellbeing, existential anxiety decreases. Moreover, there is significant and negative relationship between optimism and existential anxiety. Put it differently, with the increase of optimism, existential anxiety decreases.The results of step-wise regression analysis indicate that, psychological wellbeing can be predicted by existential anxiety. That is to say that, 45 percent of existential anxiety can be predicted by psychological wellbeing. In the second step, results indicated that, optimism can be predicted by existential anxiety. That is to say that, 23 percent of existential anxiety can be predicted by psychological wellbeing and optimism.