LncRNAs play an important role in a variety of biological processes, such as cancer pathogenesis. The lncRNA zinc ribbon domain containing 1 antisense RNA 1 (ZNRD1-AS1) is a natural antisense transcript of ZNRD1. In this study, we found that ZNRD1-AS1 levels were significantly upregulated in gastric cancer tissues compared to those in adjacent healthy gastric tissues. ZNRD1-AS1 levels were correlated with lymph node metastasis, distal metastasis, and TNM stage, but were not correlated with age and sex. ZNRD1-AS1 knockdown suppressed cell proliferation, migration, and invasion, and promoted apoptosis. ZNRD1-AS1 overexpression had the opposite effect. ZNRD1-AS1 knockdown suppressed tumor growth and pulmonary metastasis in a nude mouse model ZNRD1-AS1 can bind to miR-9-5p and ZNRD1-AS1 knockdown can decrease the protein level of heat shock protein 90 alpha family class A member 1 (HSP90AA1), which is the target of miR-9-5p. The miR-9-5p inhibitor rescued the effect of ZNRD1-AS1 knockdown, and the mutant of miR-9-5p binding site on ZNRD1-AS1 sequence blocked the effect of ZNRD1-AS1 overexpression. In conclusion, ZNRD1-AS1 levels were upregulated in gastric cancer tissues, and knockdown of ZNRD1-AS1 suppressed gastric cancer cell proliferation and metastasis by targeting the miR-9-5p/HSP90AA1 axis. Our findings provide novel insights into the mechanism underlying the role of ZNRD1-AS1 in gastric cancer.