The study presents research results in the level of phonemic awareness, particularly phonemic analysis and synthesis at children of preschool age in connection with the level of chosen cognitive functions. The study focuses more on the cognitive function of speech, namely active vocabulary and we identify whether the active vocabulary of a preschooler in Slovakia influences the level of phonemic awareness in the field of phonemic analysis and synthesis. From the results it is clear that there is a statistically significant relation between the level of phonemic awareness in the field of phonemic analysis (r = 0,510; p= [less than]0,001) and also with the phonemic synthesis (r = 0,482; p= [less than]0,001) and active vocabulary of children. The results show that the children, who achieved a higher level of active vocabulary, achieved also the higher level of perceptual analysis and synthesis. Thus, the findings showed that the children who achieved a higher level of active vocabulary, they also achieved a higher level of perceptual analysis and synthesis. Perceptual analysis and synthesis are the key factors of phonemic awareness that are according in a close relation with acquisition of reading and writing skills. That children entering schools with strong linguistic knowledge learn to read and write with an ease and less difficult than their peers who have lower level of vocabulary and language structures. Spoken expression is an important factor in development of a child not only in relation with actual developmental level but as a factor that can predict success of the child in school. The didactic level benefits from the research with the findings that systematic development of vocabulary of preschool children can play a significant role in development of phonemic skills of the children and furthermore, by phonemic awareness development it is possible to contribute towards developing reading and writing skills. Thus, the reading literacy can be supported.