Formula milk (PASI) is milk made from cow's milk or artificial milk whose composition has been changed so that it can be used as a substitute for breast milk. Lack of knowledge from mothers makes mothers always give PASI to their babies. The aim is to find out the knowledge of mothers in giving formula milk to babies aged 0-6 months. So that researchers are interested in researching the Relationship between Mother's Knowledge and Giving PASI to Infants aged 0-6 Months in 2019. The research design was descriptive analytic with cross sectional approach, namely a research method by measuring or observing at the same time. Population of 267 people. The sample in this study were 160 mothers who had babies aged 0-6 months. Analysis of the data in this study was statistical analysis using the bivariate test at a significance level of 95% (P <0.05) so that it could be seen whether or not there was a statistically significant relationship. The results of the study, the majority of mothers knowledge about PASI good 35%, 41.9% enough. The majority of PASI was given to infants aged 0-6 months, 48.7%, 36.9% enough. There is a significant relationship between maternal knowledge and PASI provision in infants aged 0-6 months, with a p-value = 0.007 (p <0.05). For health workers in the work area of ​​Puskesmas Sawo, North Nias Regency, they should improve the quality of service by providing counseling programs to mothers about the importance of exclusive breastfeeding so that mothers do not rush to provide additional food to their babies.