Gastric cancer (GC) is a kind of malignancy originating from the epithelium of gastric mucosa. Long noncoding RNAs (lncRNAs) are tightly related to the GC progression.Herein, our research was meant to investigate a novel lncRNA thymidylate synthetase opposite strand (TYMSOS) in GC. Quantitative real-time polymerase chain reaction was used to analyze TYMSOS expression in GC cells. 5-Ethynyl-2ʹdeoxyuridine, flow cytometry analysis, and transwell assay detected the influence of TYMSOS on GC cell proliferation, apoptosis, migration, and invasion. Subcellular fractionation and fluorescent in situ hybridization assays determined the cellular localization of TYMSOS in GC cells. Bioinformatics programs, RNA-binding protein immunoprecipitation, RNA pull-down, and luciferase reporter assays measured the molecular interplays of TYMSOS in GC cells. In brief, TYMSOS was highly expressed in GC cells, and TYMSOS silence inhibited GC cell proliferation, migration, and invasion while elevating cell apoptosis. Functionally, TYMSOS functioned as a competing endogenous RNA to posttranscriptionally modulate GC progression. TYMSOS interacted with miR-4739 to regulate its target gene zinc finger protein 703. Collectively, our study proved the tumor-promoting role of TYMSOS in GC cells, which might offer the utility value for GC treatment.gastric cancer (GC) has been ranked as the fifth most frequently occurred cancer and the third death cause related to cancers globally (Smyth et al., 2020). In terms of the risk factors, some found that racial and ethnic minorities, as well as smokers, face higher risks of GC (Kumar et al., 2020). In the last few years, great efforts have been made in diagnostic and therapeutic techniques. However, the overall survival of patients with GC remains dismal, the median survival being less than 1 year (Smyth et al., 2020). Increasing reports have C Cell ell B Biology iology I International nternational