A meta-analysis was performed to examine the efficiency and safety of trastuzumab in patients with advanced gastric and gastroesophageal cancer (AGC). By searching multiple databases from 1990 to March 2016, all randomized controlled trials (RCTs) which compared the effect of trastuzumab-combined chemotherapy (TC) versus chemotherapy alone (CT) in gastric cancer would be included. Five RCTs with a total of 875 patients were included. Trastuzumab can improve the overall survival (OS) rate, progression-free survival (PFS), one-year survival rate, two-year survival rate and overall response rate (ORR) of patients with AGC. There were no difference between the two arms in terms of grade 3/4 adverse effects, such as vomiting, nausea, neutropenia, thrombocytopaenia and anemia. Diarrhea increased in TC group. Trastuzumab can significantly improve the survival rate, PFS, ORR of patients with AGC. It is safe and feasible and can be tolerated. It needs further prospective multinational multicenter RCTs with large samples to define the clinical benefits of trastuzumab.