microRNA-21 (miRNA-21) is a well-characterized oncogenic miRNA in human cancers. In the present study, we found that miRNA-21 was upregulated, while long noncoding RNA Mortal Obligate RNA Transcript (lncRNA MORT), which has been reported to be silenced in 16 types of cancers, was downregulated in tumor tissues than in adjacent healthy tissues of patients with ovarian carcinoma. Expression of lncRNA MORT in tumor tissues was found to be significantly affected by tumor size but not by tumor metastasis. Expression levels of lncRNA MORT and miRNA-21 were significantly and inversely correlated in both tumor tissues and adjacent healthy tissues. Overexpression of lncRNA MORT inhibited miRNA-21, while miRNA-21 overexpression failed to significantly affect lncRNA MORT expression. Overexpression of lncRNA MORT inhibited, while miRNA-21 overexpression promoted the proliferation of cells of ovarian cancer cell lines. In addition, miRNA-21 overexpression partially reversed the inhibitory effects of lncRNA MORT overexpression on cancer cell proliferation. However, overexpression of lncRNA MORT showed no significant effects on cancer cell migration and invasion. Therefore, lncRNA MORT was downregulated in ovarian carcinoma and lncRNA MORT overexpression inhibited cancer cell proliferation, possibly by downregulating miRNA-21.