This study was performed to identify the proliferation and to measure the alteration of alkaline phosphatase activity in human gingival fibroblasts cultured. For the present study, the authors cultured the human gingival fibroblasts oriented from the sound interdental gingiva, and used third passage. It was used methyl $[^3H]$ Thymidine to identify the proliferation in human gingival fibroblasts and used 410nm of the spectrophotometer to measure the alteration of the alkaline phosphatase activity in human gingival fibroblasts. The results were as follows: 1. There was a statistically significant increase in the proliferation of gingival fibroblasts following low level laser irradiation at 24 hour(p<0.05). 2. There was a statistically significant increase in activity of alkaline phosphatase compared to control group at 5-day laser irradiation after in laser irradiation groups(p<0.05). And there was a statistically significant increase in activity of alkaline phosphatase compared to control group at 7-day laser irradiation after in the I-minute laser irradiation group(p<0.05), but there was a statistically significant decrease in activity of alkaline phosphatase compared to 1minute laser irradiation group at 7-day laser irradiation in the 2-minute laser irradiation group after(p<0.05). The results, within the limits of the present experiments, suggest that, the low level laser irradiation accelerates the proliferation of gingival fibroblasts and alters the alkaline phosphatase activity until the restricted period.