Today, children with an autism spectrum disorder are often included in regular educational institutions, so it is important to create optimal conditions for the implementation of inclusive practice. The attitudes of preschool teachers and their sense of readiness to work are the main determinants of successful inclusion. A preschool teacher who is ready and trained to work with children with an autism spectrum disorder makes it possible to adequately meet their needs, learn social and communication skills, and increases the feeling of belonging to a group. The aim of this study was to examine knowledge and stigma among preservice teachers towards autism spectrum disorder and in what relation they are with regard to the age, work experience with a child with autism spectrum disorder and educations. Also, this study examined the preschool teacher's perception of their own abilities to work with children with autism spectrum disorders. 266 preschool teachers from various preschool institutions in the Republic of Croatia participated in the research. Data were collected using the Autism Stigma and Knowledge Questionnaire (ASK-Q; Harrison et al., 2017), which was translated and adapted to the Croatian language, and the Questionnaire on self-assessed competence for working with children with autism spectrum disorder that was created for the purpose of this research. The results showed that all preschool teachers have good knowledge and have no stigma toward autism spectrum disorder. There was age difference between preschool teachers with respect to knowledge and stigma. Differences on other factors were not confirmed. When assessing their own competence to work with children with autism spectrum disorder, preschool teachers gave neutral to slightly negative answers. The correlation between self-assessment and knowledge and stigma was not confirmed. The obtained results provide an insight into the quality of implementation of inclusive practice in Croatia and indicate the need to provide additional support to preschool teachers.