Keratinized ginigva has clinical singificance in periodontal health because it plays important roles in resistance to mechanical trauma, to penetration of bacteria, and to tensional stress by muscle attachment. In order to investigate the width change of anterior keratinized gingvial during transitional period, the width of kerainized gingiva on anterior teeth was measured annually in elementary school children with deciduous dentition until the successive anterior teeth were completely erupted. The distance from the gingival margin on mid-portion of crown to mucogingival junction was measured by Boley gauge(Hu-Friedy, U.S.A.) and was recorded as the width of keratinized gingiva. The difference of the width of keratinized gingiva according to sex and dentition was analyzed statistically by Student t-test. Following results were obtained : 1. In deciduous dentition, it was shown that the width of keratinized gingiva on maxillary central incisors($3.28{pm}0.83mm$) was the widest(p<0.01), and that on maxillary lateral incisors, mandibular central and lateral incisors was $2.69{pm}0.86mm$, $2.51{pm}0.71mm$, $2.43{pm}0.68mm$, respectively. 2. In mixed dentition, it was shown that the width of keratinized gingiva on maxillary central incisors ($5.10{pm}0.86$) was the widest(p<0.01), and that on maxillary lateral incisors, mandibular central and lateral incisors was $4.35{pm}0.83mm$, $3.51{pm}0.60mm$, $3.57{pm}0.66mm$, respectively. 3. The width of anterior keratinized gingiva was significantly increased after the successive anterior teeth were completely erupted(p<0.001). The width of keratinized gingiva on maxillary central and lateral incisors, and mandibular central and lateral incisors was increased by $1.82{pm}0.83mm$, $1.65{pm}0.69mm$, $0.99{pm}0.39mm$, and $1.14{pm}0.98mm$, respectively. 4. There was no statistical significance in the difference of the width of anterior keratinized gingiva between male and female(p>0.05).