Sarcopenia (defined as low skeletal muscle index - SMI) and myosteatosis (defined as low skeletal muscle radiodensity - SMD) associate with poor outcomes in gastric cancer, but their impact after robotic surgery is unknown.This retrospective cohort study analyzed 381 gastric cancer patients undergoing robotic surgery from December 2019 to October 2022. Sarcopenia and myosteatosis were assessed on preoperative CT scans. Outcomes were postoperative complications, mortality, survival, and recurrence. Multivariable regression and propensity score matching examined associations.The mean age at diagnosis was 58.5 ± 10.8 years, and 69.3% (262/381) were male. Low SMI or Low SMD independently associated with more complications (odds ratio[OR] = 3.36, 95%CI: 2.08-5.43; OR = 2.49,95%CI: 1.48-4.19, respectively), unplanned ICU admission (OR = 1.51, 95%CI: 1.22-8.44; OR = 2.00; 95%CI: 1.23-8.89, respectively) or 30-day mortality (OR = 5.89, 95%CI: 1.80-14.23; OR = 7.34; 95%CI: 2.43-18.67, respectively). Concurrent sarcopenia and myosteatosis heightened risks of complications (OR = 7.29, 95%CI: 1.62-42.30), severe complications (OR = 6.67, 95%CI: 2.22-12.68), 30-day mortality (OR = 9.55, 95%CI: 2.67-33.89), and reduced survival (hazard ratio[HR] = 3.09, 95%CI: 1.77-8.60).Sarcopenia and myosteatosis independently and additively associate with increased postoperative complications, mortality, and worse prognosis after robotic gastric cancer surgery. Identifying sarcopenia and myosteatosis preoperatively could inform risk assessments and guide management to improve surgical outcomes.© 2025. The Author(s).