PPIL1 was identified as a member of cyclophilin family several years ago (Ozaki et al., 1998; Mann et al., 1998). PPIL1 is similar to cyclophilins in the PPIase ability and could be inhibited by cyclosporin. In the past few years, PPIL1 has been found as a member of spliceosome in the activated form (Makarov et al., 2002) coexisting with SNW/ SKIP. Pre-mRNA splicing, the excision of introns from mRNA precursors, is a prerequisite for the expression of most eukaryotic genes. Major structural changes occur in the spliceosome during its activation just before catalyzing the splicing of hnRNAs. SNW/SKIP may aid in conformational transition of the gene expression machine through its recruiting appropriate effector molecules, such as the prolyl isomerase PPILs (Folk et al., 2004). So PPIL1 may play an important role in the processing of transition of spliceosome. It was found that the PPIL1–SKIP/ SNW interaction was not affected by cyclosporin, the potent inhibitor of PPIase. Thus, PPIL1– SKIP/SNW interaction seems not to occupy the prolyl isomerase catalytic site. But the mode of interaction is still unknown (Skruzny et al., 2001). In PDB, there is a crystal structure of the cyclophilin B from Homo sapiens having about 47% identity and 67% similarity to hPPIL1, which is with the highest identity and similarity in publications (Mikol et al., 1994). Here we report the backbone and side chain assignments of hPPIL1 as the first step in the study of its full 3D structure, which could provide the platform for the interaction of hPPIL1 with its substrates.