Aptamers are in vitro evolved molecules that bind to target proteins with high affinity and specificity by adapting three-dimensional structures upon binding. Because cancer cells exhibit the activation of signaling pathways that are not usually activated in normal cells, RNA aptamers against such a cancer cell-specific signal can be useful lead molecules for cancer gene therapy. The Wnt/β-catenin signaling pathway plays important roles in a critical initiating event in the formation of various human cancers. Because mutations in β-catenin have been found to be responsible for human tumorigenesis, β-catenin is the molecular target for effective anticancer therapies. Here, we describe the selection of RNA aptamers against β-catenin/transcription factor (TCF) proteins and their intracellular expression as intramers. The RNA aptamers acted as central inhibitory players for multiple oncogenic functions of β-catenin in colon cancer cells. These data provide the proof-of-principle for the use of RNA aptamers for an effective anticancer gene therapy.