CIAPIN1 is a newly identified anti-apoptosis molecule which plays an important role in definitive haematopoiesis in mouse fetal liver and confers multidrug resistance in gastric cancer cells. However, the biophysical function of CIAPIN1 is far from elucidated. Bioinformatics predicts that CIAPIN1 may contain a generic methyltransferase motif and a Zn-ribbon-like motif. Based on these data, we postulated that CIAPIN1 might be a DNA or RNA methyltransferase. To substantiate this proposal, recombinant human CIAPIN1 (rhCIAPIN1) was expressed by a baculovirus-insect cell system and purified by Ni-NTA affinity chromatography. In vitro DNA and RNA methyltransferring tests, DNA demethylation test and S-adenosyl-l-[methyl-3H]methionine (3H-AdoMet) binding test were carried out. Our experiments failed to demonstrate that rhCIAPIN1 had any DNA, RNA methyltransferase activity, DNA demethylase activity, or had the capability of binding AdoMet in vitro. Further studies are needed to definitely clarify whether CIAPIN1 has methyltransferase activity.