ObjectiveObesity has been associated with chronic low‐grade systemic inflammation. This study aimed to investigate the relationship of pentraxin‐3 (PTX‐3) with anthropometric measurements, dietary content and physical activity level in children.DesignA matched group study.PatientsThis study was conducted with 91 children aged 6–17 years, divided into two groups: “non‐obese group” (Body Mass Index Standard Deviation Score [BMI SDS] <95th percentile) and “obese group” (BMI SDS ≥95th percentile).MeasurementsPlasma PTX‐3 levels.ResultsThe mean age of 91 children included in the study was 12.34 ± 2.86 years. Plasma PTX‐3 levels were significantly higher in obese children (p = .028). No significant correlation was found between BMI SDS and plasma PTX‐3 values, but a weak positive correlation was found when physical activity level was controlled (r = .176, p = .049). In addition, it was found that fat mass was a partial mediator of plasma PTX‐3 level, and an increase in the amount of subcutaneous adipose tissue negatively affected plasma PTX‐3 level. Plasma PTX‐3 level showed a weak positive correlation (r = .223, p = .017) with physical activity score and dietary polyunsaturated fatty acid intake, while a weak negative correlation with neutrophil‐to‐lymphocyte ratio. One unit increase in physical activity score or polyunsaturated fatty acid level caused 0.730 and 2.061 unit increases in plasma PTX‐3 level, respectively; while one unit increase in dietary fat intake caused 0.413‐unit decrease.ConclusionThere was an indirect relationship between the amount of subcutaneous adipose tissue and PTX‐3 level. The results of our study suggested that plasma PTX‐3 was associated with lower levels of inflammation in children.