Obesity is now becoming a global problem, causing many life threatening lifestyle diseases. The burden is even more worrying among the young children in the developing countries like Kenya because few studies have been done. The purpose of the study was undertake an assessment of Obesity prevalence and precipitating factors among lower primary school children in Likoni Sub County, Mombasa County, Kenya. The study employed a descriptive cross sectional study and the school children of between grade 1-4 in both private and public schools being the target population. Sample sizes of 384 participants were recruited using Cochrans (2010) formula. Structured questionnaire was used to collect quantitative data, observational checklist and anthropometric measurements were used to collect qualitative data. Data was analyzed using SPSS version 20 and interpreted using tables and pie charts. The study findings show that obesity stands at 23% among respondents. According to BMI interpretations there were 2% under weight, 69.1% normal in public schools, while over weight (28.1) and obesity (32.6%) was high in private school children. There was a significant association between means of transport (p=0.000), leisure time (p=0.000), Grade (0.000), residence (0.000) occupation (0.000) and income (p=0.000). The determinants to obesity in children were residence (AOR 29.46; CI 10.054, 86.34) and between break meals (AOR 4.647; CI 1.958,11.025).