Background The association between parental perception of child's weight and their attitudes towards his/her dietary habits has not been reported yet. This study aimed to assess the association between parental underestimation of child's weight and parental attitudes towards child's dietary habits. Methods We conducted a cross-sectional analysis of SENDO cohort participants recruited between January 2015 and June 2020. All information was collected through online questionnaires completed by parents. We calculated crude and multivariable-adjusted odds ratio (OR) and 95% confidence intervals (CI) for unhealthy attitudes towards child's dietary habits associated with parental underestimation of child's weight. Results Sixteen percent of children in the SENDO project had parents who underestimated their weight. Parents who underestimated their child's weight status were more likely to have unhealthy attitudes toward his/her dietary habits [OR 3.35; 95% CI (1.71-6.53)]. Conclusions Parental underestimation of child's weight was associated with unhealthy attitudes towards child's dietary habits. Pediatricians and public health practitioners should pay attention to the parental perception of child's weight to identify parents who underestimate it as an at-risk group in which to inquire about lifestyle and dietary habits.