C/EBP beta (CCAAT/enhancer-binding protein beta) is an important transcription factor involved in cellular proliferation and differentiation. Overexpression of the full-length C/EBP beta protein results in cellular growth arrest and apoptosis. Using a nonviral liposome as carrier, we delivered the full-length C/EBP beta expression plasmid, pCN, into nude mice bearing CW-2 human colon cancer tumors via tail vein. Southern blots revealed that the major organs and tumors were transfected. Experimental gene therapy showed that a strong suppression of tumor growth was observed in the pCN-treated mice, and such suppression was due to the overexpression of C/EBP beta, leading to the increased apoptosis in tumors of pCN-treated mice. No apparent toxic effects of pCN/liposome complex were observed in the animals. Thus, C/EBP beta has tumor suppression effect in vivo and may be used in gene therapy for cancers.