Objective: This study aimed to compare posttraumatic stress symptoms (PTSS), depression and family functioning between families of children with cancer and families of healthy children, examine the relationships among children’s PTSS, parents’ PTSS and depression, and family functioning, and explore the effect of disease experience on PTSS and the association between pain and PTSS in children with cancer. Methods: Participants were children with cancer (n=91) and their parents (n=91), and healthy children (n=114) and their parents (n=96). The children were asked to self-report PTSS and self-rate their pain degree, and the parents completed self-reported measures of PTSS, depression, and general family functioning. Results: The prevalence of severe PTSS in parents of children with cancer (21.98%) was significantly higher than that in parents of healthy children (1.04%). No significant difference was found in the total PTSS scores between children with cancer and healthy children. The children’s PTSS was positively correlated with their parents’ PTSS and depression in cancer group but not in the control group. Family functioning affected children’s PTSS in both families of children with cancer and healthy families. In children with cancer, PTSS was positively correlated with pain during cancer treatment but not correlated with disease experience. Conclusions: Children with cancer perceive the fear of pain during cancer treatment, whilst their parents experience more psychological trauma. Apart from cancer treatment, attention should also be given to pain management in children with cancer and the mental health of the entire family.