This research is a quantitative study carried out to determine the knowledge, attitudes and practices of expectant mothers towards sibling jealousy and the jealousy behaviors observed in their children using a relational search model. The study group consisted of 390 hospitalized mothers in the Gynecology Clinic of a University Hospital between August 2015 and August 2016. The data were collected using surveys developed by the researchers after the required permissions were obtained according to the ethical guidelines. The basic data such as the participants' knowledge about sibling jealousy, the methods they used to avoid it and their demographic information were presented with frequency and percentage tables. In order to determine the relationship between the mean scores of current jealousy behaviors of the children and those after learning that they would have a new sibling, the t test, one of the parametric tests, was applied because of the normal distribution of the data obtained after the assumptions of normality were examined. As a result of the statistical procedures, almost all of the mothers (94.6%) said to have informed the big sibling about their pregnancy, most of the participants (58.5%) had information to avoid jealousy among the siblings, more than half of them (52.3%) did not get any information about childrearing before, and those who did mostly got it from television/ the internet. In our study, it was observed that sibling jealousy is more common in siblings with a higher average age and in girls. Besides, it is more common among the children whose mothers aged 35 years and under and high school graduates and the sibling jealousy behaviors after the baby came home were found to be significantly lower than those after learning that they would have a new sibling.