Purpose: The purpose of this study was to investigate the influencing factors of post-traumatic growth in patients with gastrointestinal cancer. Methods: A cross-sectional study was conducted, enrolling 120 patients with gastrointestinal cancer. Their general characteristics, disease-related characteristics, perceived illness intrusiveness, levels of optimism, social support, and post-traumatic growth were assessed through self-administered questionnaires. The collected data were analyzed using descriptive statistics, independent t-test, oneway ANOVA, Pearson's correlation, and multiple regression analysis. Results: The mean score of post-traumatic growth was 52.74 points(total score of 92 points). Among the subscales of post-traumatic growth, levels of the preciousness of life were the highest, and relating with others was the lowest. The post-traumatic growth was found to be significantly correlated with optimism (r=.48, p<.001), social support (r=.47, p<.001), and depression (r=-.37 p<.001). Factors associated with post-traumatic growth were optimism (β=.36, p<.001), social support (β=.31, p<.001), and depression (β=-.27, p<.001). Conclusion: Given that prevalence of gastrointestinal cancer is increasing in Korea, identifying general, psychological, and social factors affecting post-traumatic growth among this population will be helpful in clinical practice. Integrated strategies to increase optimism and social support and lower depression should be considered to improve the post-traumatic growth of patients with gastrointestinal cancer.