Research objective: This study was conducted to assess the clinical features, x-ray characteristics of proximal primary molar teeth caries in children from 5-8 years. Research subjects: Children aged 5-8 years diagnosed with proximal caries of primary molars at the hight technic centre of odontoStomatology-Hanoi medical University and department of peadiatrics of Hanoi National odontoStomatological Institut from April - Oct, 2013. Research methods: Cross-sectional descriptive study. Results and conclusions: In 119 patients, the authors found that there are 369 primary molars with proximal tooth caries (38.76 percent). The majority of caries position located between two primary molars (86.3 percent). The first lower primary molars are the most frequently occured of this lesion (86.30 percent). The pulpitis rate is especialy high (42.8 percent) and most of its has complication of apical inflammation. X-ray images showed that the distance between floor of caries hole and pulp horn is about 1-2 mm. Bitewing x-ray is useful for detection proximal tooth caries early.