Long noncoding RNAs (lncRNAs) encompass short open reading frames (sORFs) that can be translated into small peptides. Here, we investigated the encoding potential of lncRNA LINC00665 in osteosarcoma (OS) cells. Bioinformatic analyses were utilized to predict the lncRNAs with encoding potential in human U2OS cells. Protein expression was assessed by an immunoblotting or immunofluorescence method. Cell viability was assessed by cell counting Kit-8 (CCK-8). Cell proliferation was detected by 5-ethynyl-2’-deoxyuridine (EdU) assay. Cell migration was gauged by transwell assay. The downstream effectors of the short peptide were verified using qualitative proteome analysis after immunoprecipitation (IP) experiments. The effect of the short peptide on protein interactions were confirmed by Co-Immunoprecipitation (CoIP) assays. We found that lncRNA LINC00665 encoded an 18-amino acid (aa)-long short peptide (named LINC00665_18aa). LINC00665_18aa suppressed the viability, proliferation, and migration of human MNNG-HOS and U2OS OS cellsin vitroand diminished tumor growthin vivo. Mechanistically, LINC00665_18aa impaired the transcriptional activity, nuclear localization, and phosphorylation of cAMP response element-binding protein 1 (CREB1). Moreover, LINC00665_18aa weakened the interaction between CREB1 and ribosomal protein S6 kinase A3 (RPS6KA3, RSK2). Additionally, increased expression of CREB1 reversed the inhibitory effects of LINC00665_18aa on OS cell proliferation and migration. Our findings show that the short peptide LINC00665_18aa exerts a tumor-inhibitory function in OS, providing a new basis for cancer therapeutics through the functions of the short peptides encoded by lncRNAs.