Adjusted water fluoridation has been disputed because of its various effects on human health. Previous studies have been concerned with the difference in bone mineral density (BMD) between water fluoridated (WF) and none water fluoridated (NWF) districts. The aim of this study is to examine whether water fluoridation affects BMD. BMD was measured by dual energy X-ray absorptiometry (DXA). 386 adults(174 males and 212 females) in Ansan (WF) district and 399 adults (176 males and 223 females) in Sihwa (NWF) district, participated in this study. The Ansan and Sihwa districts are similar in residential environment and living class. The relationship between serum fluoride concentration and BMD was also examined by analysis of the serum fluoride concentrations from 402 inhabitants of the Ansan district. In females, the BMD of subjects living in Ansan ($0.457{pm}0.008$) was a little higher than that of Sihwa subjects ($0.446{pm}0.008$), although it is not significant, after adjusting for BMI, physical activity level, educational achievement, smoking volume, menopause status, and number of births. However, the BMD of Ansan subjects ($0.532{pm}0.020$) in their forties was statistically higher than that of Sihwa (0.498{pm}0.019). No relationship was found in males. In residential periods, there was significant difference (Ansan $0.467{pm}0.013$, Sihwa $0.434{pm}0.012$, p=0.0125) in the BMD between females of two districts, particularly in the group of over 6 year long-term inhabitants. On the contrary, there was no remarkable difference in males from the two districts. Serum fluoride concentrations in females were associated with BMD, especially in the age group of forties (p=0.0457). No relationship was observed in the male group. Analysis of adult BMD over the age of 20 in a water fluoridated and a none water fluoridated district, confirms more or less a higher BMD in the water fluoridated (WF) district, especially for females. It is assumed that the difference between two districts came somewhat from the effect of water fluoridation.