Background: Exposure to sunlight is vital for the synthesis of vitamin-D and vitamin D plays an important role in growth and bones strength. Therefore, this study aimed to assess the knowledge and practice of infants exposure to sunlight among lactating women. Methods: A cross-sectional study was conducted from May 01 to 30, 2019 among 327 infant coupled lactating mothers attended at Yirgalem General Hospital. An interviewer-administered questionnaire was used to collect relevant data through a convenient sampling technique. Results: A total of 84.7% of respondents exposed infants to sunlight. More than 94% knew the benefit of exposing infants to sunlight. About 20.9%, 25.6%, and 19.9% of mothers exposed infants to sunlight within 15, 16 to 30, and 31 to 45 days of birth, respectively. In addition, 59.9% of respondents exposed infants to sunshine daily and 72.2% exposed without clothing the infants’ body. Moreover, 63.5% of mothers have applied lubricants and overall 54.5% of mothers exposed infants to sunlight in good practice. Unemployed women were 4.7 times more likely (aOR; 95%CI: 4.7; 2.0-11.4) to expose infants to sunlight when compared to those employed, while women whose husbands have at least secondary education level were 5.1 times more likely (aOR; 95%CI: 5.1; 1.6-16.1) to expose infants to sunlight when compared to those unable to read and write. Conclusion: More than 45% and more than one-third of lactating mothers had poor practice and exposed infants to sunlight for inadequate time, respectively. Therefore, the finding indicates a need for awareness creation to increase women’s knowledge and practice toward the exposure of infants to sunlight.