Purpose of study: Research was conducted on 61 pupils living with premature primary molar loss at the Nguyen Trai school - Ha Dong - Hanoi in 2011. The purpose of study is aim to describle somes of clinical characteristics and affected factors on dental arch diagnosed premature primary molar loss. Research methodology: cross-sectional descriptive study, clinical examination and on the plaster cast. Results: In the group of premature primary molar loss in the maxillary, the highest Angle II rate is accounted for 76 percent, the percentage of first molars malocdusion in the arch with premature primary molar loss is 87 percent, In the group of premature primary molar loss, the over bite 2mm is 63.93 percent. Conclusion: premature primary molar loss in the maxillary, malocclusion usually is Angle II, the premature primary molar loss in the mandible, malocclusion usually is Angle III. The premature primary molar loss cause malposition of first molar.