The mRNA was isolated and purified from tree shrew (TS) liver tissue. A cDNA library of the liver tissue was then constructed by using the mRNA as the template by reverse transcription. Two apolipoprotein CI (apoCI) cDNA clones were identified in the library with an anti-serum to TS apoCI. Sequencing and analysizing of the clones showed that both were the apoCI cDNA sequences in which the larger one was determined as 380 nucleotides. It contains 21 bp and 95 bp in 5' and 3' untranslated regions respectively, and 264 bp in an open reading frame, encoding an 88 aa apoCI precursor (a 26 aa signal peptide, and a 62 aa mature protein whose length is the same as those of rat, mouse and dog, but longer than those of human and baboon by 5 aa residues). The function domains in the protein sequence deduced from the cDNA were predicted by comparison of conservative regions in apoCIs from different species. The results of Northern blot indicated in TS the presence of apoCI mRNA not just mainly in the liver but also found in the intestine, suggesting the mRNA distribution different from those in other mammals and primates.