This thesis presents an action research conducted with a group of children (age 5 to 7) as a part of a larger action research about music activities in preschool, conducted in altogether three groups of children in the same preschool institution. Being aware of the rare occurrence of musical activities in the group as well as multiple benefits of self-initiated and self-organized activities for the entire child development, preschool teachers began an action research on self-organized musical and musical-creative activities of children. The research was conducted in three stages. In the first stage, the objective was to enrich the physical environment of the music center in their room. In the second stage preschool teachers changed their strategies and practice while organizing and conducting music activities, and the third stage was focused on collaborating with music professionals in order to provide as many different musical experiences for children as possible. Self-organized musical activities of children and the effects of changes made in educational process on their appearance, content and course was followed during the research. Participation in this research led to the professional development of all adult participants. Also, it significantly improved the quality of children's stay in preschool. Research findings indicate that the stimulating physical environment, as well as active participation of children in creating their educational process, and the adequate and unobtrusive stimulating by preschool teachers, are likely to influence the increase of the frequency of self-initiated and self-organized musical activities of children in the educational process. Research also confirms the contribution of self-initiated and self-organized musical activities to development of the child's musical-creative expression. Thereat, the role of preschool teachers as an instigator and observer, as opposed to the role of the interpreter, is emphasized. This can eliminate the insecurity of preschool teachers caused by the fear of failure and incompetence while conducting musical activities in their educational practice.