Abstract: This study aimed at investigating the nature of the psychological stress experienced by secondary school students in Al-Khobar district and the relationship between psychological stress and optimism and pessimism. Moreover the study aimed at identifying any significant differences in psychological stress ascribed to the variables of school specialization and academic achievement, and to identify the most important variables that can predict psychological stress among students. The study followed the descriptive analytical method and used two tools: the measure of Psychological Stress prepared by the researcher consisting of (60) items divided into five dimensions (psychological stress, school stress, family stress, physical stress, social stress) and The Arab List for Optimism and Pessimism prepared by Ahmed Abdul-Khaliq (1996) which consists of (30) items distributed equally between optimism and pessimism. The study population consisted of the (5020) high school students in public schools in Al-Khobar district in the academic year (1432-1433). The sample consisted of (502) students who were randomly selected from the population (10%). Results revealed the following main results: The students of high schools suffered from a moderate level of psychological stress and the most stress experienced was school stress, followed by emotional stress, social stress, family stress, and physical stress respectively. There were statistically significant differences in the school stress among high school students ascribed to the variable of the grade in favor of the first and third secondary grade students compared to the second secondary students while no significant differences were identified on the rest of the dimensions ascribed to the students grade. There were significant differences in psychological stress in general, emotional psychological stress, family stress and physical stress ascribed to the variable of academic achievement in favor of low achievers. There was a negative statistical significant correlation between psychological stress and optimism (-.268) and a positive statistical significant correlation between psychological stress and pessimism (0.448). The results of the regression analysis showed that the best predictor of psychological stress is pessimism which explained (20%) of the variation followed by pessimisin and academic achievement which together explained (% 0.07) of the variation in psychological stress.