As an adjunct to cancer treatment, the use of health functional foods (HFFs) seems to be increasing. However, little is known for the use of HFFs among cancer patients in Korea. The aims of this study were to investigate the exposure rate of HFF use among gastrointestinal (GI) cancer patients and to examine the relationship of socio-demographic and disease-related characteristics with the use of HFFs. A total of 126 patients diagnosed with GI cancer participated in the study. A cross-sectional survey was conducted using a questionnaire. Over a half of all the patients surveyed (n = 67; 53.2%) used HFFs. Patients who were younger, had higher income, or longer duration of disease showed a trend to use HFFs more frequently, even though the tendency was not statistically significant. The most commonly used HFF was vitamin complex (n = 20; 16%), followed by red ginseng (n = 15; 12%), and sweet wormwood (Artemisia annua) (n = 11; 8.8%). About 26% of all responders expressed concerns for using HFFs. The primary concern was 'going against physician's recommendations' (36.8%). About 63% of respondents expressed a desire to consult with their physicians and follow their recommendations. More basic scientific data and educational materials regarding HFFs are required for both health-care professionals and cancer patients. A larger sample and size-controlled groups representing each cancer type will continue to be recruited for participation in this survey.