Purpose: To explore the psychological experiences of the family caregivers of inpatients with gastric cancer or colorectal cancer, and to identify the relationships among insecure attachment, social support, and psychological experiences. Methods: The study design is a cross-sectional quantitative study collecting data through the use of four questionnaires, including the Hospital Anxiety & Depression Scale, the Self-esteem subscale of the Caregiver Reaction Assessment Scale, the Experience in Close Relationship Scale and the Social Support Rating Scale. Hierarchical regression analysis and path analysis were used to analyze the collected data. Results: Data from 207 participants was used. Family caregivers had experienced both depression and high self-esteem. Social support has significant direct effects on both depression and self-esteem. Attachment anxiety had direct effects on depression and social support, attachment avoidance had direct effects on self-esteem and social support. Social support has mediated the relationship between adult attachment and psychological experiences. Conclusions: Caregivers had experienced both negative and positive psychological outcomes. There were differences in the effects of insecure attachment on psychological experiences. Social support plays an important role in the relationships among insecure attachment, depression, and self-esteem. Insecure attachment styles and social support should be considered in tailored interventions for family caregivers to reduce their depression and enhance their self-esteem.