The class A scavenger receptor (SR-A) is a glycoprotein expressed on the cell surface of macrophages that mediates internalization of chemically modified lipoprotein. It was reported that the receptor internalization required the presence of internalization signal motif and the rate of receptor internalization was governed by the pattern of receptor phosphorylation induced by the ligands. However, the role of the cytoplasmic domain played in the receptor-mediated endocytosis is not fully characterized. Here the changes in internalization process of the receptor were reported when the whole cytoplasmic domain sequence (150 base pairs) was truncated. Both the full length and truncated were recombinated into PcDNA3.1/HisB vector and were then transfected to CHO cells separately. Measurement of uptake of DiI-AcLDL by transfected cells with FACS showed that the bind and uptake of the ligand in full length SR-A was higher than that of truncated receptor(1.3 fold increase).After incubated with DiI-acetyl-LDL (DiI-AcLDL), the full length SR-A-transfected cells showed a diffuse distribution of the DiI-AcLDL in cytoplasm as well as in cell membrane when monitored under laser confocal microscopy. But in the truncated SR-A-transfected CHO cells, DiI-AcLDL mostly distributes at the cell surface only. In order to elucidate the role of phosphorylation played in mediating the function of cytoplasmic domain of SR-A, transfected CHO cells were preincubated with Staurosporine for 1 h at the concentration of 0.4 μmol/L. Then the cells were refed with medium containing DiI-AcLDL at the concentration of 10 mg/L at 37℃ for 2 h, the DiI specially associated to cells was measured by spectrofluoremeter. The result indicated that staurosporine did not changed DiI-AcLDL bound and untaken by truncated receptor, which was different from the full length SR-A that increased obviously. The research here demonstrated that cytoplasmic domain regulate the receptor activity of SR-A, in which the phosphorlation or dephosphorlation of the cytoplasmic domain might play a key role,the MSR-A cytoplasmic domain may be indispensable in mediating binding and uptaking as well as internalization.