Chitosan, with a chemical structure similar to hyaluronic acid, has been implicated as a wound healing agent. The purpose of this research was to evaluate the effects of chitosan on the characteristics of periodontal ligament cells, calvaria cells and gingival fibroblasts and to define the effects of chitosan on bone formation in vitro. In control group, the cells were cultured alone with Dulbecco's Modified Eagle's Medium contained with 10% Fetal bovine serum, 100unit/ml penicillin, 100microgram/ml streptomycin, 0.5microgram/ml amphotericin-B. In experimental group, chitosan(40microgram/ml) is added into the above culture condition. And then each group was characterized by examining the cell proliferation at 1, 3, 5, 7, 9, 12, 15 day, the amount of total protein synthesis, alkaline phosphatase activity at 3, 7 day and the ability to produce mineralized nodules of rat calvaria cell at 11 day. The results were as follows: 1. At early time both periodontal ligament cells and calvaria cells in chitosan-treated group proliferated more rapidly than in non-treated control group, but chitosan-treated group of periodontal ligament cells at 9 days and calvaria cells at 12days showed lower growth rate than control group. Gingival fibroblast in chitosan-treated group had lower growth rate than in control group but the difference was not statistically significant (P< 0.01). 2. Both periodontal ligament cells and calvaria cells in chitosan-treated group showed much protein synthesis than in control group at 3 days, but showed fewer than in control group at 7 days. Amount of total protein synthesis of gingival fibroblast didn't have statistically significant difference among the two groups(P< 0.01). 3. At 3 and 7 days, alkaline phosphatase activity of periodontal ligament cells and calvaria cells was increased in chitosan-treated group, but at 7 days there was not statistically significant difference among the two groups of calvaria cells (P< 0.01). Alkaline phosphatase activity of gingival fibroblast didn't have statistically significant difference among the two groups(P<0.01). 4. Mineralized nodules in chitosan-treated group of rat calvaria cells were more than in control group. In summery, chitosan had an effect on the proliferation, protein systhesis, alkaline phosphatase activity of periodontal ligament cells and calvaria cells, and facilitated the formation of bone. It is thought that these effects can be used clinically in periodontal regeneration therapy.