Recently I discovered that preschool education has evolved from integration of various subject contents and working methods. The purpose of my study is to investigate preschool teachers' attitudes and ways of working with a theme-oriented approach. I also want to examine their opinions regarding the integration of subject content in terms of mathematics and science subjects (NO) in preschools theme-oriented work approach. My questions for this study are: What is a preschool teacher's attitude and their ways of working to a thematic-oriented approach? What is a preschool teacher's opinions regarding the integration of subject content, especially in mathematics and science subjects (NO) in their pre-schools theme-oriented work approach? I have used myself a qualitative method of investigation to produce materials for my research project. I collected my empirical material for my study from the semi-structured interviews that was done with four preschool teachers in two preschools in Botkyrka municipality. As for my theoretical perspective, I used John Dewey's well-known knowledge theory called “Learning by doing”, which he indicated as learning through practical work. These working methods based primarily on children’s experience and subject integration. My conclusion is that the four preschool teachers worked thematic in the preschool children in a natural way.  In fact, the thematic-oriented approach appeared in two different work situations (planned and unplanned work situations) in the pre-school. The four preschool teachers developed and improved their own professional skills in the working process and also the children's knowledge and learning skills by prioritizing the children's interests, needs and circumstances. It came to my understanding that both mathematics and science subjects content were integrated in a conscious way in these preschools thematic-oriented approach. The preschool teachers integrated the two subject contents through their creative and joyful way of working. The idea was that the children's curiosity, knowledge, experience and awareness can be raised through various activities and experiments. Hence through the subject integrated approach, the children develop both their skills and conceptual understanding of both subjects content.