<p>Childhood obesity and bullying are interconnected public health issues that negatively influence both, physical and mental health. Stress could be an explanatory mechanism mediating the relationship between bullying victimization and obesity. Thus, this study aims to investigate whether hair cortisol levels mediate the association between bullying and weight status. Participants were 11-year-old preadolescents from the INMA project in Spain (<i>N</i> = 465). Bullying was assessed using the Olweus Bully Victim Questionnaire (OBVQ), while weight status was determined based on Body Mass Index (BMI) and body fat percentage. To study the complex associations path analysis was carried out. In terms of bullying prevalence, 8.6% of the participants were involved as victims, 1.7% as bullies and 2.4% as bully/victims. Regarding weight status, 24.9% of the participants were overweight and 11.4% had obesity. Results partially confirmed the main hypothesis, as a mediating effect of hair cortisol between involvement in bullying and body fat percentage was identified in boys, specifically those who were victims (<i>X</i>² (1) = 0.326; <i>p</i> = 0.982; CFI = 1.00; RMSEA = 0.000; <i>p</i> = 0.987). Understanding this association is crucial for elucidating the mechanisms that may exist between bullying and some physical consequences of this phenomenon such as overweight or obesity.</p>