N6‐methyladenosine (m6A) modification regulatory proteins are involved in the development of many types of cancer. KIAA1429 serves as a scaffold in bridging the catalytic core components of the m6A methyltransferase complex. The role of KIAA1429 in gastric cancer and its related mechanism has not been reported upon. The expression of KIAA1429 was detected in human gastric cancer tissues and cell lines by quantitative real‐time polymerase chain reaction and western blot. The effects of KIAA1429 on gastric cancer proliferation were evaluated by cell counting kit assays, colony formation assays, flow cytometry assay, and in vivo experiments with nude mice. And messenger RNA (mRNA) high‐throughput sequencing, RNA immunoprecipitation assay (RIP), luciferase assay, and a rescue experiment were used to identify the relationship between KIAA1429 and its specific targeted gene, c‐Jun. We found that KIAA1429 was upregulated in gastric cancer tissues, and expressed lower in adjacent tissues. The upregulated KIAA1429 promoted proliferation and downregulated KIAA1429 was proved to inhibit proliferation of gastric cancer in vitro and in vivo. Then, we identified the potential KIAA1429 regulating gene as c‐Jun by mRNAs high‐throughput sequencing and RIP assay. By luciferase assay, we verified that KIAA1429 regulated the expression of c‐Jun in an m6A‐independent manner. Finally, the overexpression of c‐Jun rescued the inhibition of proliferation caused by KIAA1429 knockdown in gastric cancer cells. KIAA1429 could act as an oncogene in gastric cancer by stabilizing c‐Jun mRNA in an m6A‐independent manner. This highlights the functional role for KIAA1429 as a potential prognostic biomarker and therapeutic target in gastric cancer. In this study, we provided in vitro and in vivo evidence that KIAA1429 played a key role in promoting gastric cancer by regulating c‐Jun expression in an m6A independent manner. This finding has the potential to develop a new therapeutic target for the treatment of gastric cancer.