The topic of this thesis is the application of Montessori didactic material in the field of mathematics in early and preschool education. Maria Montessori, the founder of the Montessori pedagogy, is the most popular name in the history of preschool education and one of the most important figures of reform pedagogy. She dedicated her life to advocating for children’s rights, their development and expression of their intellectual abilities. Her teaching is based on the scientific observation of the spontaneous learning of children, on the encouragement of the child's own actions, independence, and personality. She observed children at different stages of development and in contact with children from different cultures. What she perceived to be common to all children, she described as universal characteristics of childhood, noticeable regardless of where the children were born or raised. She began to act as an advocate for children, advising adults to approach children in a new way and treating each childhood period as a separate entity, not just as preparation for adulthood. She divided the life of an individual from birth to the age of 18 into three periods: from birth to 6 years, from 6 years to 12 years, and from 12 to 18 years. She divided each of these periods into two intermediate periods, developed practical exercises using special didactic materials, and documented instructions for working with children. She divided her didactic materials into five areas: material for practical life exercises, material for stimulating sensory abilities, material for language, material for mathematics, and material for cosmic education. This paper explains in more detail the application of Montessori didactic material in the field of mathematics conducted with pre-school children at the Cekin Kindergarten in Slavonski Brod.