We showed that upregulation of lncRNA RGMB-AS1 was significantly correlated with differentiation, TNM stage, and lymph node metastasis. In lung adenocarcinoma cells, downregulation of lncRNA RGMB-AS1 inhibited cell proliferation, migration, invasion, and caused cell cycle arrest at the G1/G0 phase. In vivo experiments showed that lncRNA RGMB-AS1 downregulation significantly suppressed the growth of lung adenocarcinoma. The expression of lncRNA RGMB-AS1 was inversely correlated with that of repulsive guidance molecule b (RGMB) in lung adenocarcinoma tissues, and UCSC analysis and fluorescence detection assay indicated that lncRNA RGMB-AS1 may be involved in the development of human lung adenocarcinoma by regulating RGMB expression though exon2 of RGMB.