OPA-interacting protein 5 antisense transcript 1 (OIP5-AS1) plays an important regulatory role in various types of cancers. However, the functional role and regulatory mechanisms of OIP5-AS1 in gastric cancer (GC) remain largely unknown. In this study, we found that the expression of OIP5-AS1 was increased in GC tissues compared with that in adjacent non-cancerous tissues, which was significantly associated with shorter overall survival time of patients. In addition, OIP5-AS1 expression was also increased in GC cell lines including NCI-N87, MKN-45, BGC-823 and SGC-7901, when compared with that in normal gastric epithelial cell line GES-1. Knockdown of OIP5-AS1 markedly suppressed the proliferation and colony formation activities of GC cells, induced G0/G1 arrest and apoptosis of GC cells in vitro, and restrained tumor growth in vivo. Mechanistically, OIP5-AS1 functions as an oncogenic competing endogenous RNA by binding to and sequestering miR-422a to elevate the expression of anoctamin-1. Our study first demonstrated that OIP5-AS1 is a critical and powerful regulator of GC pathogenesis and may represent a novel candidate target for GC therapy.