Since the one-child policy was implemented in China in 1979, many investigators have studied the psychological consequences to children without siblings. Although the results are not conclusive, there is evidence that children who have siblings, rather than only children, have increased anxiety and depression. Whether the differences between students with and without siblings would continue when they reached university age is an interesting question. We used the Zuckerman–Kuhlman Personality Questionnaire to assess personality traits and the Plutchik–van Praag Depression Inventory to measure depressed mood in 134 university students with and 126 university students without siblings. Most students without siblings (93.7%) were reared in urban areas, while 90.3% of students with siblings came from rural areas. Parental professions were higher in social status and annual family incomes were higher in students without siblings. Increased neuroticism–anxiety, aggression–hostility, and depressed mood were found in students with siblings. Gender and annual family income were not significantly related to personality in the two groups, and birth-order position was not related to personality in the students with siblings. In contrast, the depression score was positively correlated with neuroticism–anxiety and aggression–hostility, but negatively correlated with parental occupation and annual family income. The greater competition to receive high education, reduced benefits from society, and lower level of social respect might nurture these personality traits in students with siblings. These findings might, in some limited aspects, indicate that the one-child policy affects personality traits and depressed mood in students with siblings.