Pregnancy is a unique period during women’s life characterized by complex physiological changes, which may adversely affect oral health. The purpose of this work was to evaluate the level of knowledge on oral health in a group of Mexican pregnant women. A questionnaire was applied to pregnant women (N = 50) undergoing prenatal medical supervision at the General Women's Hospital in Zacatecas, Mexico, during the period November 2015-February 2016. The general level of knowledge that a group of pregnant women have about oral health was evaluated, including preventive measures, oral diseases, dental care and dental development. The X2 test was used to analyze the level of knowledge regarding age, place of origin and level of education. It was found that 58% of respondents have a regular level of knowledge on oral health. Furthermore, 44% of respondents had a regular knowledge about preventive measures. Poor level of knowledge was found in the areas of oral diseases, dental care and dental development. Statistically significant differences were observed between the level of knowledge about physical health, age (p = 0.0008) and the place of origin of the pregnant women (p = 0.0266). Oral health education during prenatal care should be a priority for health services, both in terms of motivation and promotion of healthy habits for the family.