Although cryopreservation has been used to keep viability of cells, it has a severe problem with damaging cells while freezing and thawing them. So we have tried long-term reservation of cells to solve the problem. In this study, we stored three kinds of cells (Hep3B, A549, 293T) in the presence of three different medium molecular weight chitosans (MMWCs) in concentration of 0.05%, 0.01%, 0.005% and 0.001%, respectively, under reservation for a certain period of time. We named them P (MW: 7.6 kDa), B (MW: 5.6 kDa), S (MW: 3.5 kDa) respectively. Then we measured viability of cells with FACS and ELISA after 2, 3 and 4 days respectively. And we measured proliferation of cells with cell proliferation ELISA, BrdU (colorimetric). Our data suggest that viability of cells increase in concentration dependent manner of MMWCs. Subsequently this study demonstrated that MMWCs (MW: 3~7 kDa)are significant factors acting in long-term reservation of cells. However MMWCs have no clear effect on proliferation of cells. Further studies are needed to perform in long-term storage of cells using MMWCs including other polysaccharides to enhance an efficiency of storage.