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Simple Summary: Metastasis, the hallmark of cancer, is accountable for about 90% of cancer-related deaths. Long noncoding RNA (lncRNA), a subset of the noncoding RNAs, has exhibited involvement in various processes, including immune evasion, cell proliferation, migration, and invasion, across multiple human diseases, notably cancer. The objective of our study was to identify a metastasis-associated lncRNA in lung cancer and elucidate the underlying mechanisms. Our findings indicate that Linc01703, which is notably downregulated in metastatic lung cancer cells, effectively suppresses lung cancer metastasis in vivo. Interestingly, Linc01703 does not directly impact the proliferation and invasion capabilities of lung cancer cells but rather inhibits cancer metastasis by promoting the secretion of CD81+ exosomes through the Rab27a/SYTL1/CD81 transport complexes. Consequently, our observations provide new insights into the potential clinical application of CD81+ exosome-based cancer therapy. Metastasis, a major cause of cancer-related mortality worldwide, frequently occurs early in the diagnosis of lung adenocarcinoma (LUAD). However, the precise molecular mechanisms governing the aggressive metastatic behavior of LUAD remain incompletely understood. In this study, we present compelling evidence indicating that the long noncoding RNA linc01703 is significantly downregulated in metastatic lung cancer cells. Intriguingly, in vivo experiments revealed that Linc01703 exerted a profound inhibitory effect on lung cancer metastasis without discernible impact on the in vitro proliferation or invasion capacities of LUAD cells. Mechanistically, Linc01703 enhanced the interaction between Rab27a, SYTL1, and CD81, consequently promoting the secretion of CD81+ exosomes. These exosomes, in turn, suppressed the infiltration of immune cells within the tumor microenvironment, thereby impeding LUAD metastasis. Importantly, our analysis of lung cancer tissues revealed a correlation between reduced CD81 expression and an unfavorable patient prognosis. Collectively, our findings suggest that Linc01703 functions as a metastasis suppressor by facilitating the secretion of CD81+ exosomes through the formation of the Rab27a/SYTL1/CD81 complex. [ABSTRACT FROM AUTHOR]