Background: Little is known about midwives’ knowledge and skills to assess and promote maternal health literacy. Aims: To test the reliability and validity of a new tool to assess midwives’ health literacy knowledge, skills and attitudes. Methods: Using a cross-sectional design, midwives were recruited through professional and social media networks. The online survey included demographic and professional questions and a new measure on midwives’ health literacy knowledge, skills and attitudes. Convergent validity was assessed using ten items from the Caring Assessment Scale. Perceived barriers to promoting maternal health literacy were sought. Findings: Three hundred and seven participants completed the survey. A two-factor solution accounted for 41% of variance and resulted in 14 items, including all attitude items, being removed. Cronbach's alpha reliability was acceptable (Skills = .76; Knowledge = .66). Convergent validity was established. Most midwives (77.1%, n = 221) reported giving limited attention to formally assessing women's health literacy. Between 30 to 60% of midwives never or only sometimes used specific techniques to promote maternal health literacy. Most (75%, n = 201) had not received education about health literacy. Discussion and Conclusions: The new Transforming Maternity Care Collaborative Health Literacy tool was valid and reliable. Few midwives formally assessed or promoted women's health literacy. Midwives require education about maternal health literacy assessment and promotion to ensure women understand information being conveyed. A large national survey of midwives using the new tool is recommended.