Gastrocolic fistula (GCF) is associated with a variety of diseases, but in recent years it has most frequently been observed with gastric or colonic malignancy. The management of primary tumor lesions and optimal surgical treatment strategies remain controversial. In this study, we explore the clinical diagnosis and treatment of GCF by retrospectively analyzing the records of GCF patients treated between August 2008 and February 2014. Three female patients and one male patient with an average age of 61 years were diagnosed with GCF caused by malignancy during this period. The predominant symptoms were diarrhea, vomiting, weight loss, and abdominal pain. Gastrointestinal contrast series combined with fiber endoscopy was the most accurate method of diagnosing the GCF, while CT and MRI were helpful in identifying the extent of tumor invasion and evaluating the possibility of en-bloc resection. Pathological and immunohistochemical tests, including staining for CK-20, CK-7, and CDX-2, suggested that three cases originated in the colon and one case in the stomach. All four cases underwent single-stage en-bloc fistula resection; two severely malnourished patients received concurrent colostomies. One patient died of postoperative anastomotic leakage and cardiopulmonary failure, but the remaining three patients were discharged in improved condition. En-bloc resection followed by adjuvant chemotherapy can result in long term survival. Gastrointestinal contrast series combined with fiber endoscopy showed high sensitivity in the diagnosis of GCF. Immunohistochemical staining can be conducted for tumors with an unclear source. Single-stage radical en-bloc fistula resection is the recommended surgical treatment, and concurrent colostomy should be considered in severely malnourished patients.