BackgroundDespite the advancement of modern treatment approaches, several studies indicated a diminished health‐related quality of life (HRQoL) in patients with gastrointestinal cancer. However, there is insufficient data about the HRQoL of gastrointestinal cancer patients in Kenya.AimsThe study aimed to investigate HRQoL and its determinants in gastrointestinal cancer patients at Kenyatta National Hospital.MethodsA cross‐sectional study was employed among 160 esophageal, 103 gastric, and 96 colorectal cancer patients. The patient list, identified by unique hospital identification numbers, was obtained from records. Eligibility was assessed based on predetermined criteria, and the hospital identification numbers were reshuffled. Study participants were then randomly selected daily during the data collection period. Data were collected using a researcher‐administered European Organization for Research and Treatment of Cancer quality of life questionnaire. The data entry and analysis were carried out using Statistical Package for the Social Sciences 26.0 statistical software. A bivariate and multivariate binary logistic regression analysis was employed to investigate determinants of HRQoL at a 0.05 level of significance.ResultsMost esophageal (N = 118, 73.7%), gastric (N = 75, 72.8%), and colorectal (N = 72, 75%) cancer patients had poor overall HRQoL. In the social (p = .04) and cognitive (p = .02) domain of HRQoL, esophageal cancer patients had a significantly lower mean score as compared to gastric cancer patients. Colorectal cancer patients had the highest mean score in physical functioning (p = .01) as compared with gastric cancer patients. Nonetheless, gastric cancer patients had the highest mean score in emotional functioning domains of quality of life as compared to esophageal (p = .04) and colorectal (p < .001) cancer patients The study revealed a low mean HRQoL score in the majority of the symptom domains of quality of life. A statistically significant difference in all domains of HRQoL was not observed in various treatment modalities of gastrointestinal cancer. Advanced‐stage (stages III and IV) and co‐morbidities were significant determinants of poor HRQoL.ConclusionsThe overall HRQoL of gastrointestinal cancer patients was poor. Advanced‐stage cancer and co‐morbidities were significant determinants of poor HRQoL. Therefore, intensification of routine monitoring of the disease and the treatments should be actively implemented to improve the HRQoL.