Introduction: Measures of parental self-efficacy (PSE) for healthy dietary or physical activity (PA) behaviors in children have been used in several studies; however, further psychometric validation of PSE for these behaviors is needed. The purpose of the present study was to evaluate the psychometric properties of a new PSE instrument. Methods: Mothers (n = 162) of 6-year-old children in the Healthy School Start prevention trial of childhood obesity responded to the instrument and a parent-report questionnaire on diet and PA in children. In addition, PA was objectively assessed by accelerometry. Results: Exploratory factor analysis yielded a structure composed of three factors of PSE for dietary and PA behaviors in children, and PSE was associated with parent-report of these behaviors. Internal consistency was good. Discussion: Preliminary support of the validity and reliability of the PSE instrument was provided. The measure may be useful in prevention and treatment trials of childhood obesity.