Long noncoding RNAs (lncRNAs) have emerged as key regulators of tumor development and progression. The lncRNA HNF1A-antisense 1 (HNF1A-AS1) is a 2455-bp transcript on chromosome 12 with a potential oncogenic role in esophageal adenocarcinoma. Nevertheless, current understanding of the involvement of HNF1A-AS1 in lung adenocarcinoma tumorigenesis remains limited. In this study, we analyzed the roles of HNF1A-AS1 in 40 lung adenocarcinoma tissues and five lung cancer cell lines. Our results showed that HNF1A-AS1 was significantly up-regulated in lung adenocarcinoma tissues compared with corresponding non-tumor tissues, and its expression level was significantly correlated with TNM stage, tumor size, and lymph node metastasis. The UCSC Cancer Genomics Browser's Kaplan-Meier plot suggested that patients in the high HNF1A-AS1 expression subgroup experienced worse overall survival compared to the low expression subgroup. Moreover, HNF1A-AS1 was determined to promote tumor proliferation and metastasis, both in vitro and in vivo, by regulating cyclin D1, E-cadherin, N-cadherin and β-catenin expression. In addition, the binding of HNF1A-AS1 to DNMT1 may explain its regulation of E-cadherin. In conclusions, we demonstrated that increased HNF1A-AS1 expression could regulate cell proliferation and metastasis and identified it as a poor prognostic biomarker in lung adenocarcinoma.