Parental knowledge about children's dental health one of them can be assessed from knowledge about the dental health problems. One of the dental health problems is malocclusion. The extrinsic factor that often leads to malocclusion is a bad oral habit. Parental ignorance about bad oral habit can be causes of dentofacial abnormalities in children, therefore parental knowledge about bad oral habit should be considered. The influence of knowledge and attention of parents against children‟s bad oral habit can determine whether this habit is done continuously or not. This research aims to find out the effects of parental knowledge level on children‟s bad oral habit. This research was an analytic observational method with a cross-sectional approach. The subjects of the research were 88 children aged 7-9 years old studying in SD Negeri Karangjati, Kasihan, Bantul, Yogyakarta with their parents. The children‟s oral cavity was examined to determine the clinical signs due to bad oral habits and questionnaires also given to the parents as the supporting data to find out children‟s bad oral habit if any, while the parents were given questionnaires to gather data of the knowledge level. The obtained data were analyzed by chi-square and binary logistic regression test. Based on the chi-square and binary logistic regression test result, there was an effect of parent‟s knowledge level on children‟s bad oral habit with p-value 0,032 (p<0,05) and Nagelkerke R2 value 0,071 which means parental knowledge level affects children‟s bad oral habit as much as 7,1%.