Introduction and objective <p>An unhealthy diet is one of the most important behavioral factors associated with the risk of progression of prediabetes to diabetes. The present study aimed to determine the effect of an educational program on WhatsApp based on the Theory of Planned Behavior (TPB) on the dietary behaviors of women with prediabetes.</p> Methods <p>A quasi-experimental study with a control group was conducted on 72 women with prediabetes referring to health centers in Mashhad, Iran. The samples were randomly assigned to two experimental and control groups. Participants in the experimental group received an 8-session educational program based on TPB via WhatsApp. Data were collected using a demographic information questionnaire and a questionnaire based on TPB constructs before, immediately after the intervention and at 3-month follow-up. Data analysis was performed using SPSS version 25 software, with a significance level of <i>p</i> &lt; 0.05.</p> Findings <p>The mean scores of attitude, subjective norms, perceived behavioral control, intention, and dietary behavior in the experimental group significantly differed from the control group from baseline to follow-up. (<i>P</i> &lt; 0.001). However, these changes were not significant in the control group.</p> Conclusion <p>The results suggest that TPB-based nutrition education via WhatsApp can promote dietary behaviors in women with prediabetes. TPB is a suitable theoretical framework for healthy behaviors and can be used to design educational interventions via social media platforms to empower patients with prediabetes.</p>