Mounting evidence demonstrates that long non-coding RNAs (lncRNAs) are novel transcripts governing multiple biological processes, and their dysregulation is involved in the development and progression of multiple types of cancers. Small Nucleolar RNA Host Gene 20 (SNHG20) is a 2183 bp lncRNA, and its overexpression predicts poor prognosis in colorectal cancer and hepatocellular carcinoma. However, the clinical relevance of SNHG20 and its molecular mechanisms affecting cancer cell phenotype have not been documented. Here, we found that SNHG20 was upregulated in non-small cell lung cancer (NSCLC) tissues compared with normal samples. Higher SNHG20 expression was significantly associated with advanced tumor, lymph node and metastases (TNM) stage and tumor size, as well as poorer overall survival. Moreover, knockdown of SNHG20 repressed NSCLC cell proliferation, migration and induced cell apoptosis. Mechanistic investigations revealed that SNHG20 could interact with EZH2 (enhancer of zeste homolog 2), thereby repressing P21 expression. Furthermore, rescue experiments indicated that SNHG20 functioned as an oncogene partly via repressing p21 in NSCLC cells. Taken together, our findings demonstrate that SNHG20 is a new candidate for use in NSCLC diagnosis, prognosis and therapy.