Background: : Childhood over nutrition, including overweight and obesity, is an emerging public health challenge in low- and middle-income countries such as Lao PDR. Rapid urbanization and lifestyle changes in cities like Vientiane Capital have contributed to a rising prevalence of childhood overweight, coexisting with persistent undernutrition. Objectives: : This study aimed to determine the prevalence of nutritional status and identify factors associated with over nutrition among private primary school students in Vientiane Capital, Lao PDR. Methodology: : An analytical cross-sectional study was conducted from March to June 2024 involving 412 students aged 6–12 years, randomly selected from ten private primary schools in Saysettha and Xaythany districts. Data collection included structured questionnaires covering socio-demographics, dietary intake (measured via Minimum Dietary Diversity for Women adapted for children), physical activity, sedentary behaviour, and parental nutrition knowledge. Anthropometric measurements were taken to calculate BMI-for-age z-scores using WHO AnthroPlus software. Multivariate logistic regression identified factors associated with underweight and overweight status. Results: : Among participants, 16.3% were underweight, 47.3% had normal weight, and 36.4% were overweight or obese. Most parents had vocational or higher education (81.1% of fathers; 71.1% of mothers). Fathers predominantly worked in farming, labor, or state sectors (56.3%), while mothers mainly engaged in private or informal employment (58.0%). Over half the children showed low nutrition knowledge (53.2%) and a roughly equal split was observed in diet quality. Physical activity assessments indicated 63.8% were sedentary, with 39.6% exceeding recommended sedentary behaviour limits. Multivariate analysis showed children older than 8 years were less likely to be underweight (AOR=0.07; 95% CI: 0.02–0.20). Unexpectedly, higher paternal education (AOR=6.65; 95% CI: 2.40–18.42) and fathers working in private/business sectors (AOR=2.14; 95% CI: 1.23–3.72) were linked to higher underweight risk. Physically active children had lower odds of overweight (AOR=0.52; 95% CI: 0.28–0.96). Conclusion: The double burden of malnutrition is evident among private school children in urban Lao PDR. Physical activity protects against overweight, while socioeconomic factors show complex associations with undernutrition. Interventions should integrate nutrition education, physical activity promotion, parental engagement, and multispectral policies to address these challenges effectively.