In recent years, sociocultural influences and changing health awareness have contributed to growing misperceptions of body weight, leading individuals to either underestimate or overestimate their body size. Inaccurate perceptions can result in inappropriate health behaviors, delayed recognition of obesity, and psychological distress. Understanding the discrepancy between objectively measured BMI and perceived body image is essential for improving awareness and developing effective health management strategies.This study aimed to examine the association between BMI-based body image perception accuracy and health behaviors and mental health indicators , and to further evaluate its relationship with metabolic syndrome components within the obese subgroup.A cross-sectional analysis of 5,504 adults aged ≥ 19 years from the 2023 National survey was conducted. Participants were classified into three groups—underestimation, accurate perception, and overestimation—based on the concordance between measured BMI and self-perceived body image. Variables included sociodemographic factors, lifestyle behaviors, mental health indicators and clinical parameters. Among obese individuals, logistic regression analyses were performed to assess the association between obesity awareness and the prevalence and odds ratios of metabolic syndrome and its individual components.The underestimation group showed higher smoking rates, lower aerobic activity, and less frequent weight control efforts compared with the accurate perception group (p<0.01). They also had a higher prevalence of hypertension and diabetes and showed greater proportions of moderate and high risk hs-CRP levels. (p<0.01) The overestimation group exhibited higher anxiety scores and lower perceived health despite greater attempts at weight reduction. Among obese adults, unawareness of obesity was independently associated with increased odds of metabolic syndrome prevalence, abdominal obesity, hypertension, and hypertriglyceridemia compared with those who recognized their obesity (p<0.01).Underestimation of body weight was linked to adverse metabolic profiles and unhealthy lifestyle patterns, suggesting that individuals unaware of their obesity may fail to engage in preventive behaviors. Overestimation, in contrast, was associated with psychological distress, emphasizing the dual burden of both types of misperception.Improving accuracy of body weight perception may promote healthier behaviors and reduce the risk of metabolic complications. In primary care, targeted strategies to enhance self-awareness could be beneficial for managing obesity.