Musashi1, a neural RNA-binding protein, plays an important role in regulating cell differentiation in precursor cells. Recently, expression of Musashi1 has been detected in human tumor tissues such as gliomas and melanomas, suggesting its involvement in oncogenic development. To determine any association between Musashi1 and the development of liver cancer, we investigated its gene expression in seven human hepatoma cell lines: HuH6, HuH7, Hep3B, SK-Hep1, HepG2, HLE, and HLF. Musashi1 mRNA expression was analyzed using the reverse-transcription polymerase chain reaction (PCR), and the PCR products were sequenced using a subcloning procedure. Musashi1 protein expression was analyzed in HuH7 and HepG2 cells by Western blot and immunofluorescence staining. Musashi1 mRNA was detected in the HuH6, HuH7, and Hep3B hepatoma cell lines, but not in the others. Sequencing of the PCR-amplified Musashi1 cDNA in these three cell lines showed the expected sequence of the human Musashi1 gene. Musashi1 protein expression was confirmed in HuH7 cells, which were positive for Musashi1 mRNA expression, but not in HepG2 cells. These results suggest that Musashi1 expression may be an important factor in the development of several types of carcinoma such as human hepatoma, and may be a useful molecular marker for tumor detection.