The purpose of this study was to examine the oral health behavior and knowledge of middle schoolers in an attempt to facilitate the selection of what to teach about oral health. The subjects in this study were 315 students at three different middle schools located in the city of Gunsan. After a self-administered survey was conducted by using structured questionnaires in collaboration with their homeroom teachers, the answer sheets from 315 students were gathered. And the answer sheets from 302 students were analyzed with SPSS 12.0 program except 13 incomplete ones. The findings of the study were as follows: 1. By gender and grade, the middle school boys(51.3%) outnumbered the middle school girls(48.7%), and the seventh, eighty and ninth graders respectively accounted for 31.5, 32.8 and 35.8 percent. 2. As to the parts of the mouth they brushed, the largest number of the seventh graders(31.6%) and ninth graders(56.5%) brushed their teeth and tongue. The largest group of the eighth graders(39.4%) brushed their teeth, tongue and gums, and the gaps between them and the others were statistically significant. 3. In regard to toothbrushing frequency, the ninth graders did that 2.62 times, which was the largest frequency, but the gap between them and the others was not statistically significant. The seventh graders got a mean of 2.95 and 3.48 on oral health behavior and knowledge respectively, and the eighth graders got 2.73 and 3.42 respectively. The ninth graders got 2.70 and 3.07. Thus, the seventh graders scored statistically significantly better than the eighth and ninth graders(p<0.01, p<0.05). As for oral health knowledge by gender, the boys and girls got 3.17 and 3.47 respectively. The latter scored significantly higher than the former(p<0.05). 4. Concerning school oral health education experiences, the rates of the seventh, eighth and ninth graders who had ever received that education stood at 69.5, 50.6 and 50.5 percent respectively, and those students significantly outnumbered the others who hadn`t(p<0.01). As to the necessity of school oral health education, they considered it necessary to receive that education from professionals irrespective of grade, but the gap between them and the others was statistically insignificant. Regarding an intention of receiving school oral health education, those who were willing to take that education statistically significantly outnumbered the others who weren`t(p<0.05). The rates of the former students in their seventh, eighth and ninth grades respectively stood at 71.6, 53.6 and 63.0 percent. 5. As for the relationship of their oral health behavior scores to toothbrushing frequency, there was a statistically significant correlation between the two(r=0.227, p<0.001). And the oral health knowledge scores had a statistically significant correlation to toothbrushing frequency (r=0.116, p<0.05) and oral health behavior scores(r=0.358, p<0.001). Therefore, it could be said that higher oral health knowledge scores led to higher oral health behavior scores and more toothbrushing frequency.