Background: Hypertension in children is one of major concerns in public health. However, there is no evidence within the Lao population. Therefore, we aimed to determine the prevalence of hypertension in children and adolescents aged 11-15 years old. Methodology: A descriptive, cross-sectional study was conducted in children and adolescents aged 11-15 years old at secondary schools of Vientiane Capital, Lao PDR. Two secondary schools were purposively selected, Vientiane and Bornagnao schools. The data were collected using questionnaire form. Result: A total of 365 students were included in the study of which 50.7% were male. The mean age was 13.7 years old (Min=11 and Max=15). The majority of students were of Lao Loum ethnicity (95.1%). Of 365 students, 140 (38.3%) had high blood pressure during the survey. Of these, 99 (27.1%) people were at pre-hypertension, 6.3% in stage 1 and 4.9% in stage 2. Most (74.5%) of included students had normal Body Mass Index (BMI). Students with overweight and obesity were significantly more likely to have hypertension than others (p<0.001). Conclusion We found a high prevalence of hypertension in secondary school students particularly in those overweight and obese. Therefore, it is important to provide appropriate education at school to reduce the risk factors as well as hypertensive screening.