Introduction It is estimated that the world population is getting older. Accordingly, the incidence of GI tract malignancies is increasing in patients over 65 years of age. This study aims to investigate the impact of frailty on the postoperative course of elderly patients with gastrointestinal malignancies (GIM). Methodology This study recruited 120 elderly patients who had been operated on for GIM. Variables such as age, readmission rate, duration of hospitalization, and frailty index (FI) criteria (fatigue, endurance, walking/running speed, comorbidities, and weight loss) were determined, and the FI was calculated. The relationship between the FI and postoperative complications in the study participants was then evaluated. Results The study involved 120 patients with gastric, colon, and rectal cancers. The mean age of the participants was 72.79 ± 5.4 years, of which 56.6% (68) were male and 43.3% (52) were female. The average hospitalization duration was 6.7 days, and the average ICU stay duration was 2.2 days. There was a correlation between the age of the patients and their FI scores (FIS). Conclusion It was determined that the FIS increases in parallel with increasing age among the elderly. Furthermore, the presence of preoperative comorbidities with old age increases postoperative mortality and morbidity.