Nonalcoholic fatty liver disease is the most common chronic liver disease and can present with advanced fibrosis or nonalcoholic steatohepatitis. The purpose of this study was to investigate the effect of a 7-day intense physical activity intervention on liver fat content in children with obesity. Fifty-seven obese children (mean body mass index: 26.5 ± 3.2 kg/m²; mean age: 12.0 ± 0.8 years) participated in a 7-day physical activity program. All participants were housed together, and their food intake and energy expenditure were strictly controlled. Anthropometric measurements, abdominal computerized tomography scans, and blood analyses were conducted at baseline and post-intervention. Participants lost weight by 2.53 ± 0.85 kg on average (61.0 ± 9.8 vs. 58.5 ± 9.5 kg, p < 0.05), fat mass (16.7 ± 5.1 vs. 15.7 ± 4.9 kg, p < 0.05), and serum insulin (13.7 ± 6.7 vs. 3.5 ± 2.0 μU/mL, p < 0.05). However, liver fat content was increased, presented as liver-to-spleen ratio (LSR) where lower LSR represents higher liver fat content. The intervention increased aspartate transaminase level (29.42 ± 6.78 IU/L vs. 33.50 ± 9.60 IU/L, p < 0.001). The change in liver fat content was not associated with the change in fasting insulin and liver enzymes. Short-term intense physical activity increased liver fat content independent of change in fasting insulin level and liver enzymes. This is the first human study to report increased liver fat content after physical activity-induced rapid weight loss.