Background: The upper gastrointestinal tumors, such as gastric adenocarcinoma (GAC) and esophageal squamous cell carcinoma (ESCC), have high rates of incidence and poor prognosis in our country, lacking of efficient therapy after failure of first-line regimen. Despite available treatment, there are still huge unmet medical needs of second-line or later-line therapy for patients with GAC or ESCC. Therefore, we will investigate the efficacy and safety of Anlotinib Hydrochloride (a multi-target tyrosine kinase inhibitor) combined with Nivolumab (PD-1 antibody) in GAC and ESCC. Methods: Patients with unresectable or metastatic GAC or ESCC who have failed standard therapy were treated by Anlotinib Hydrochloride 12mg/day orally for two weeks and Nivolumab 360mg every 3 week until the disease progression or intolerable adverse effects occurring. The study protocol was registered on ClinicalTrial.gov (NCT04503967,07/08/2020). The primary endpoint of this study was ORR (Objective Response Rate). The secondary endpoints were PFS (Progression-Free Survival), OS (Overall Survival), DCR (Disease Control Rate), and safety. Results: Gastric adenocarcinoma cohort would be reported only. From December 2020 to September 2022, 45 patients were enrolled in gastric adenocarcinoma cohort. There were 34 male patients and 11 female patients. The median age was 59 years. The percentage of gastric cancer patients with second-line and later-line treatment were 62.2% and 37.8%, respectively. 2 patients (4.4%) achieved complete remission (CR), 11 patients (24.4%) got partial remission (PR), and 15 patients (33.3%) got stable disease (SD). The ORR (CR+PR) was 28.9%, and DCR (CR+PR+SD) was 62.2%. Among 28 patients (62.2%) treated as second-line therapy, ORR was 32.1%, and DCR was 57.0%. As for later-line therapy of 17 patients, ORR and DCR were 23.5% and 70.6%, respectively. The median follow-up duration was 15.0 months (95% CI 8.17~21.83), then median PFS was 3.80±0.94 months, and median OS was 11.10±3.04 months. When the patients were treated as second-line therapy, median PFS was 3.0±0.97 months, and median OS was 14.50±3.89 months. Median PFS and OS in later-line patients of gastric adenocarcinoma were 3.80±1.30 months and 8.0±0.68 months, respectively. 36 patients (80%) had treatment-related adverse events (TRAEs). More than 10% of incidence rate included hypothyroidism (n=8), liver dysfunction (n=6), and rash (n=6). G3-4 of TRAEs were hypothyroidism (n=1), liver dysfunction (n=1), palmar-plantar erythrodysesthesia (n=1), rash (n=1), and hypophysitis (n=1). Conclusions: Anlotinib hydrochloride combined with Nivolumab showed effective clinical response and tolerable safety in second-line or later-line treatment of advanced gastric adenocarcinoma. Clinical trial information: NCT04503967.