Background: It has been well documented that long non-coding RNAs (lncRNAs) regulate numerous characteristics of cancer, including proliferation, migration, metastasis, apoptosis, even metabolism. LncRNA BCYRN1 (BCYRN1) is a newly identified brain cytoplasmic lncRNA with 200-nucleotide, which was discovered highly expressed in tumor tissues of cancer, including hepatocellular carcinoma, gastric cancer and lung cancer. However, the roles of BCYRN1 in colorectal cancer (CRC) remain obscure. This study was designed to reveal the acts of BCYRN1 in the occurrence and progression of CRC.Methods: RT-PCR was used to detect the expression level of BCYRN1 in tumor tissues and CRC cell lines. Knock down BCYRN1 in CRC cells, evaluate cell proliferation changes by CCK-8 test, EdU test, and Ki-67 and PCNA expression; evaluate cell migration and invasion changes by wound healing assay, Transwell assay and invasion-related protein expression . Through flow cytometry analysis to assess whether BCYRN1 regulates apoptosis of CRC cells. The dual luciferase reporter gene detects the competitive binding of BCYRN1 to miR-204-3p. In vivo experiments to evaluate the effect of BCYRN1 on tumor development. TargetScan analysis and dual luciferase reporter gene detect the target gene of miR-204-3p. Rescue experiments verified the effect of BCYRN1 on CRC by regulating the effect of miR-204-3p on KRAS.Results: We found that compared with normal tissues and human intestinal epithelial cells (HIECs), BCYRN1 levels were significantly increased in tumor tissues and cell lines of CRC. We further determined that knockdown of BCYRN1 inhibited proliferation, migration, invasion, and promoted apoptosis of CRC cells. In addition, bioinformatics analysis and dual luciferase reporter assay showed that BCYRN1 served as a competitive endogenous RNA (ceRNA) to regulate the development of CRC through competitively binding to miR-204-3p. Further studies proved that overexpression of miR-204-3p reversed the effects of BCYRN1 on CRC. Next, TargetScan analysis and dual luciferase reporter assay indicated that KRAS was a target gene of miR-204-3p and negatively regulated by miR-204-3p. A series of rescue experiments showed that BCYRN1 affected the occurrence and development of CRC by regulating the effects of miR-204-3p on KRAS. In addition, tumorigenic experiments in CRC model mice confirmed that down-regulated BCYRN1 effectively inhibited tumor growth. Conclusions: Our findings suggested that BCYRN1 plays a carcinogenic role in CRC by regulating the miR-204-3p/KRAS axis.